SPOILER WARNING: This article contains major spoilers for "The Real Deal," the 100th episode of Agents of S.H.I.E.L.D.
Peterson appeared to Coulson when the S.H.I.E.L.D. agent went to confront a rip in space-time created by destruction of three Kree monoliths. The explosion that destroyed the monoliths created a doorway into what Fitz described as a "fear dimension," which conjured up manifestations of their worst fears. So, as Coulson approached the fear dimension's doorway, he wasn't expecting to run into a friendly face like Peterson's.
"Hello, Agent Coulson," Peterson called out in greeting. "It's time I told you what's really going on here." The ghost of Peterson told Coulson it was time to face facts. "That this is all in your head," he explained. "I'm telling you that you've never been to T.A.H.I.T.I. Or Malta, or Puerto Rico, or outer space, or the Framework, or the future. You're on the table, Coulson. Code blue."
"This whole thing has been a dream, and every time the dream is too random or doesn't reconcile with a memory, your mind creates a scenario to make it work," he continued. "You really think your skull caught on fire, Phil? Or does it hurt to have electrodes on your scalp for this long? Do you think there was an alternate reality where you were a history teacher, or were you remembering your father, who was a history teacher? You're reliving momentos of your life mixed with the dreams you wished had come true."
"You're struggling to let go," he said. "That's why your mind created this story, where you spent years doing all the things you never got a chance to do. To vacation on a white beach with blue water. To travel to the stars. To own your own plane, a car that flies. Your own team. To have a family, the brilliant students you never got a chance to mentor. The daughter you never had. And above all, the chance to be a hero. You said it yourself, Coulson: it matters who you are."
"Even now, your mind is rejecting the fact that I'm just an EMT standing over you. It's trying to make me into something else," he insisted.
Even as this fake Peterson tried to convince Coulson that this chapter of his life had been a dream, the real Deathlok arrived at the Lighthouse in a quinjet full of other S.H.I.E.L.D. allies. Coulson had secretly sent Deke out to rally the troops earlier in the episode, and the man out of time delivered.
Peterson got violent when Coulson refused to "go to the light" with him, but Deathlok turned up just in time to save him. With a blast from his cyborg enhancements, Deathlok destroyed the manifestation of himself and took on others like Lash, Hive and the Vrellnexians. This enabled Coulson to set off Fitz's gravity device, which temporarily closed the tear in space-time. Deathlok also saved Coulson from being sucked into the fear dimension when the device activated. After the violent episode, Deathlok also stuck around for Fitz and Simmons' impromptu wedding, though he didn't intend to stay beyond that because "he rolls solo."
The return of Mike Peterson and Deathlok brings Agents of S.H.I.E.L.D. full circle in its own way. Richards debuted the character in the pilot episode of the series, so it's only fitting that he returned to give Coulson a helping hand 100 episodes later. Deathlok's arrival also spat in the face of Coulson's worse fear, in that Coulson impacted the lives of those he has helped enough that they would come back to help him in return.
Airing Fridays at 9 p.m. ET/PT on ABC, Marvel’s Agents of S.H.I.E.L.D. Season 5 stars Clark Gregg, Ming-Na Wen, Chloe Bennet, Henry Simmons, Ian De Caestecker, Natalia Cordova-Buckley and Elizabeth Henstridge.