Alex Mercer: the Crazy- between parkour, being a living arsenal, and not having a moral compass, perfect for suicide missions. Also the ability to perfectly copy people is useful.
Special Agent Francis York Morgan: the Brains- master investigator and 'people person'. Also incredibly good at throwing people off balance, with a quiet word.
Natasha "The Black Widow" Kerensky- the Heavy- nothing like a Dire Wolf piloted by one of the best trueborn warriors in the Periphery.
Captain John Sheridan: The Leader- he's the man you'd follow into Hell, against anything, because he doesn't sacrifice people in vain, and does what needs to be done, no matter the cost, but without sacrificing his humanity.
Hellboy: Man of Action- doesn't play by the rules, doesn't like seeing people suffer, and he's seen the worst the supernatural has at hand (whether it be the undead, armies led by witches, or demons of all shapes and sizes) and they still haven't killed him.
Lord Henry Baltimore: The Stalwart- will fight to his last breath, and doesn't give a damn about numbers. Will hold the line, giving time for the rest of the team to complete their mission.
Mordin Solus: The Doc- whether its super plagues, abominations of flesh and steel, or the armed and unruly, he's useful to have at hand, because he always a solution, whether scientific or practical (gun to the face).