Phil Coulson: A S.H.I.E.L.D. agent who oversees many of the division's field operations. In April 2013, Gregg agreed to join the series after hearing Whedon's explanation for Coulson's resurrection, following the character's death in The Avengers, which he called "fascinating" and "true to the world of the comics and mythology". On whether the resurrected Coulson would be the same as before he died, Gregg said that the character had to have changed in some way, but he may not understand how much he has changed. Gregg said that he approached Coulson's promotion to Director of S.H.I.E.L.D. as being his dream job, which at the same time forced the character to adopt a more sensible and level-headed attitude, such as that of Nick Fury.
Ming-Na Wen as Melinda May: A S.H.I.E.L.D. ace pilot and weapons expert, nicknamed "the Cavalry". Joss Whedon had the character, who was originally listed with the name Agent Althea Rice on casting sheets, "rolling around in his head" for a long time. Wen was given some backstory for the character to prepare, but was not told how she gained her reputation; with May's past revealed in "Melinda", Wen called it "devastating ... To have learned what she had to do, for the good of the many ... I can understand why it would traumatize her so much and cause her to retreat." Wen called May "unconventionally maternal", and found that it is her loyalty and platonic love for Coulson rather than any feelings about S.H.I.E.L.D. that make her stay in the organization.
Brett Dalton as Grant Ward and Hive: Ward is a Hydra agent who poses as a S.H.I.E.L.D. black ops specialist. From the conception of the series it was decided that he would be a traitor, with Jed Whedon explaining that they wanted to have "infiltration based on betrayal" on a small scale to represent the same thing happening on a massive scale, and to make the Hydra reveal more personal for the characters. Following the death of his Hydra superior, John Garrett, Dalton explained that he felt that Ward was always loyal to Garrett rather than Hydra, and so without Garrett would become more of a wildcard, eventually accepting his position as an antagonist to S.H.I.E.L.D. He is killed by Coulson in season three, and his body is possessed by the ancient Inhuman Hive. Austin Lyon portrays a young Ward.
Chloe Bennet as Daisy "Skye" Johnson / Quake: An Inhuman hacktivist and S.H.I.E.L.D. recruit who eventually becomes an agent with the ability to sense vibrations and create earthquakes. The character of Skye was always intended to be the MCU version of Johnson, with Tancharoen noting that the reveal would have consequences for the character's relationships, especially with Coulson. Bennet felt that the character was someone who would wear her heart on her sleeve, but she also has some control over her emotions. Wen noted that the character evolves from being "anti-establishment into suddenly being someone who wants to create an establishment that would help" the Inhumans. During the third season, the character no longer goes by "Skye", and by the end is known as "Quake" to the public.
Iain De Caestecker as Leo Fitz: An agent of S.H.I.E.L.D. who specializes in engineering, especially weapons technology. De Caestecker, in describing the character, said that "He’s quite passionate about what he does ... [but] he doesn’t really understand emotions as much". Fitz has a lot of interaction with Simmons in the series, with De Caestecker explaining that "they’ve got this kind of weird chemistry together, and they just kind of fit each other in a very weird way." Following injuries the character receives at the end of the first season, the series deals with brain trauma. The writers researched the issue with doctors and experts before approaching it in the series, while De Caestecker did his own research, feeling it is "something that should never be trivialized. It's a real and serious thing to a lot of people, brain trauma, so we just have to constantly be respectful towards it."
Elizabeth Henstridge as Jemma Simmons: A S.H.I.E.L.D. biochemist who specializes in life sciences (both human and alien). Henstridge described her character as "intelligent and focused and curious...she’s got a wonderful relationship with Fitz. They kind of bounce off each other." As Fitz and Simmons begin to spend time apart during the series, Henstridge noted that it "brings a whole new dynamic just to them as characters in discovering what it's like to have to be independent" since they have been near inseparable since first meeting. On the harsher side of Simmons seen later in the second season, Henstridge noted that the character has "always been very mathematical in a way". After Simmons is trapped on the planet Maveth for six months, she becomes "profoundly different", with Henstridge saying, "she doesn’t just completely change. But she’s been through so much. She’s hardened. She’s had to face things that she never would’ve imagined, also by herself without Fitz, so she’s ... stronger and kind of damaged."
Nick Blood as Lance Hunter: A mercenary before agreeing to join S.H.I.E.L.D. On his character joining the cast in the second season, Blood explained "Lance doesn’t really care that much of what people think of him....He doesn’t bow down to the etiquette of the S.H.I.E.L.D. hierarchy." He later elaborated that the character feels very independent, so would probably not want to admit no longer feeling like an outsider. Also, "he doesn't have too much respect for authority and titles...if Coulson does something he respects, that's all good. If he doesn't, he's going to say something." On Hunter's on-again, off-again relationship with Bobbi Morse, Blood said, "there is a lot of truth in it of those relationships you have where it's kind of, 'can't live with each other, can't kill each other'".
Adrianne Palicki as Bobbi Morse: Hunter's ex-wife and an agent of S.H.I.E.L.D. who spent time undercover within Hydra. Palicki was approached by the showrunners specifically for the part during season two, and at first hesitated to take the role given that she likely could not play another MCU character if she did. Palicki already had martial arts and gun training, but had to learn to use the character's signature arnis sticks; she noted similarities between Morse's fighting style and that of Scarlett Johansson's Black Widow from the MCU films. Bell said of the character, "she and Hunter have been keeping secrets from one another, evidently for years" and something about her is that she seems to be more loyal to an idea than anything else, so what may seem in the short term as a betrayal by her is usually for what she sees as the greater good.
Henry Simmons as Alphonso "Mack" MacKenzie: A S.H.I.E.L.D. mechanic with a distrust of the alien and superhuman. On the different dynamic that a mechanic brings to the S.H.I.E.L.D. team, Simmons felt that his character would not have to deal with the same stress as the other agents, and that Mack is more worried about contributing in his own way and getting his job done away from the field. About Mack's stance on violence, Simmons confirmed that Mack does not like violence, but will do "what he has to do." Mack reveals in the third season, "It’s not something I talk about but ... I rely on my faith", implying that he is a Christian. This was seen by Dee Hogan of The Mary Sue as "a refreshingly positive portrayal of people of faith, as Mack demonstrates the quiet confidence and love rather than the aggression and bigotry that’s so often associated with it."
Luke Mitchell as Lincoln Campbell: An Inhuman with the ability to manipulate electrical charges. The character was introduced because the series already featured "a guy with no eyes" and "a woman who now is covered in thorns" but, like the X-Men, there are also Inhumans who are "just attractive people with powers", and so Campbell represents them in the series. On casting Mitchell, Bell said "Luke just really impressed us ... [he] had a nice quality, and we felt he might be a good person to sort of usher Skye into this other world."
John Hannah as Holden Radcliffe: A transhumanist who believes in the improvement of humanity through enhancement. Radcliffe originally worked with Hive upon his abduction before joining S.H.I.E.L.D. where he begins work on transferring his artificial intelligence AIDA to a Life Model Decoy, an old S.H.I.E.L.D. project.
Ming-Na Wen as Melinda May: A S.H.I.E.L.D. ace pilot and weapons expert, nicknamed "the Cavalry". Joss Whedon had the character, who was originally listed with the name Agent Althea Rice on casting sheets, "rolling around in his head" for a long time. Wen was given some backstory for the character to prepare, but was not told how she gained her reputation; with May's past revealed in "Melinda", Wen called it "devastating ... To have learned what she had to do, for the good of the many ... I can understand why it would traumatize her so much and cause her to retreat." Wen called May "unconventionally maternal", and found that it is her loyalty and platonic love for Coulson rather than any feelings about S.H.I.E.L.D. that make her stay in the organization.
Brett Dalton as Grant Ward and Hive: Ward is a Hydra agent who poses as a S.H.I.E.L.D. black ops specialist. From the conception of the series it was decided that he would be a traitor, with Jed Whedon explaining that they wanted to have "infiltration based on betrayal" on a small scale to represent the same thing happening on a massive scale, and to make the Hydra reveal more personal for the characters. Following the death of his Hydra superior, John Garrett, Dalton explained that he felt that Ward was always loyal to Garrett rather than Hydra, and so without Garrett would become more of a wildcard, eventually accepting his position as an antagonist to S.H.I.E.L.D. He is killed by Coulson in season three, and his body is possessed by the ancient Inhuman Hive. Austin Lyon portrays a young Ward.Chloe Bennet as Daisy "Skye" Johnson / Quake: An Inhuman hacktivist and S.H.I.E.L.D. recruit who eventually becomes an agent with the ability to sense vibrations and create earthquakes. The character of Skye was always intended to be the MCU version of Johnson, with Tancharoen noting that the reveal would have consequences for the character's relationships, especially with Coulson. Bennet felt that the character was someone who would wear her heart on her sleeve, but she also has some control over her emotions. Wen noted that the character evolves from being "anti-establishment into suddenly being someone who wants to create an establishment that would help" the Inhumans. During the third season, the character no longer goes by "Skye", and by the end is known as "Quake" to the public.
Iain De Caestecker as Leo Fitz: An agent of S.H.I.E.L.D. who specializes in engineering, especially weapons technology. De Caestecker, in describing the character, said that "He’s quite passionate about what he does ... [but] he doesn’t really understand emotions as much". Fitz has a lot of interaction with Simmons in the series, with De Caestecker explaining that "they’ve got this kind of weird chemistry together, and they just kind of fit each other in a very weird way." Following injuries the character receives at the end of the first season, the series deals with brain trauma. The writers researched the issue with doctors and experts before approaching it in the series, while De Caestecker did his own research, feeling it is "something that should never be trivialized. It's a real and serious thing to a lot of people, brain trauma, so we just have to constantly be respectful towards it."
Elizabeth Henstridge as Jemma Simmons: A S.H.I.E.L.D. biochemist who specializes in life sciences (both human and alien). Henstridge described her character as "intelligent and focused and curious...she’s got a wonderful relationship with Fitz. They kind of bounce off each other." As Fitz and Simmons begin to spend time apart during the series, Henstridge noted that it "brings a whole new dynamic just to them as characters in discovering what it's like to have to be independent" since they have been near inseparable since first meeting. On the harsher side of Simmons seen later in the second season, Henstridge noted that the character has "always been very mathematical in a way". After Simmons is trapped on the planet Maveth for six months, she becomes "profoundly different", with Henstridge saying, "she doesn’t just completely change. But she’s been through so much. She’s hardened. She’s had to face things that she never would’ve imagined, also by herself without Fitz, so she’s ... stronger and kind of damaged."
Nick Blood as Lance Hunter: A mercenary before agreeing to join S.H.I.E.L.D. On his character joining the cast in the second season, Blood explained "Lance doesn’t really care that much of what people think of him....He doesn’t bow down to the etiquette of the S.H.I.E.L.D. hierarchy." He later elaborated that the character feels very independent, so would probably not want to admit no longer feeling like an outsider. Also, "he doesn't have too much respect for authority and titles...if Coulson does something he respects, that's all good. If he doesn't, he's going to say something." On Hunter's on-again, off-again relationship with Bobbi Morse, Blood said, "there is a lot of truth in it of those relationships you have where it's kind of, 'can't live with each other, can't kill each other'".
Adrianne Palicki as Bobbi Morse: Hunter's ex-wife and an agent of S.H.I.E.L.D. who spent time undercover within Hydra. Palicki was approached by the showrunners specifically for the part during season two, and at first hesitated to take the role given that she likely could not play another MCU character if she did. Palicki already had martial arts and gun training, but had to learn to use the character's signature arnis sticks; she noted similarities between Morse's fighting style and that of Scarlett Johansson's Black Widow from the MCU films. Bell said of the character, "she and Hunter have been keeping secrets from one another, evidently for years" and something about her is that she seems to be more loyal to an idea than anything else, so what may seem in the short term as a betrayal by her is usually for what she sees as the greater good.
Henry Simmons as Alphonso "Mack" MacKenzie: A S.H.I.E.L.D. mechanic with a distrust of the alien and superhuman. On the different dynamic that a mechanic brings to the S.H.I.E.L.D. team, Simmons felt that his character would not have to deal with the same stress as the other agents, and that Mack is more worried about contributing in his own way and getting his job done away from the field. About Mack's stance on violence, Simmons confirmed that Mack does not like violence, but will do "what he has to do." Mack reveals in the third season, "It’s not something I talk about but ... I rely on my faith", implying that he is a Christian. This was seen by Dee Hogan of The Mary Sue as "a refreshingly positive portrayal of people of faith, as Mack demonstrates the quiet confidence and love rather than the aggression and bigotry that’s so often associated with it."
Luke Mitchell as Lincoln Campbell: An Inhuman with the ability to manipulate electrical charges. The character was introduced because the series already featured "a guy with no eyes" and "a woman who now is covered in thorns" but, like the X-Men, there are also Inhumans who are "just attractive people with powers", and so Campbell represents them in the series. On casting Mitchell, Bell said "Luke just really impressed us ... [he] had a nice quality, and we felt he might be a good person to sort of usher Skye into this other world."
John Hannah as Holden Radcliffe: A transhumanist who believes in the improvement of humanity through enhancement. Radcliffe originally worked with Hive upon his abduction before joining S.H.I.E.L.D. where he begins work on transferring his artificial intelligence AIDA to a Life Model Decoy, an old S.H.I.E.L.D. project.