When he found out, he said--after already having been fitted for his costume without any knowledge of what that costume would look like--he tried to prep for the work by reading up on Deathlok, particularly the Michael Collins iteration of the character, upon whom Richards's Mike Petersen seems to be, at least loosely, based.
"Everything with Marvel is on a need-to-know basis, so I didn’t officially know [I was going to be Deathlok] until the second episode I did, which I think was the 10th episode in the season," Richards said. "Information is carefully guarded over there. I definitely didn’t know that I was Deathlok. I even had a costume fitting, and I didn’t know what I was being fitted for!"
"In my reading, I was drawn more to the Michael Collins version because this character is such a good man, such a good moral, decent person," Richards added. "For [Peterson] to do the things he’s asked to do as Deathlok are very difficult for him. When I showed up to play the character for the first couple of days, I was still trying to find it. Obviously these are circumstances that I can’t relate to, but I had to really use my imagination to get at what it would be like for Mike Peterson to be turned into Deathlok. Once I figured it out, it was like night and day, just a huge epiphany on what was going on internally for this character. I feel blessed that I’ve been asked to play this character because I always want to play the person behind the superhero."
In the comics, Collins was an employee of Roxxon Oil (you remember them from Iron Man 3 and the S.H.I.E.L.D. pilot, right? Easter eggs are important, people!), who found out about some unethical practices and then found himself betrayed after blowing the whistle to the wrong guy. Think Monsters, Inc., when Mike and Sulley go to Mr. Waternoose--who is orchestrating the crimes--to report them and end up banished--except instead of banishment, Collins ended up with his brain trapped inside the Deathlok cyborg.
In the TV series, Richards's Mike Peterson character volunteered for a Captain America-like Super Soldier treatment using the Extremis technology from Iron Man 3--and ultimately ended up trapped under the thumb of Centipede, a group of villains who have recurred throughout Agents of S.H.I.E.L.D.'s first season. After befriending and then betraying Coulson's S.H.I.E.L.D. team, Peterson was apparently killed--only to turn back up with cybernetic bits in his body.