WARNING: The following contains major spoilers for "The End Is at Hand" and "What We're Fighting For," the Agents of S.H.I.E.L.D. series finale.
Agents of S.H.I.E.L.D. just bid goodbye to Deke Shaw.
In "What We're Fighting For," the series finale, Director Alphonso "Mack" Mackenzie and the team faced a difficult decision. They could return to their original timeline and bring the Chronicoms with them, thus saving the new timeline, but there was a catch: someone had to stay behind. Ultimately, Deke chose to stay, and his sacrifice got the team back to the Marvel Cinematic Universe proper.
As Fitz attempted to explain how they would return to their original timeline, Coulson interjected. "We can't leave," he said flatly. Fitz protested, so Coulson went on to say, "I mean we can't abandon these people. We can't leave with the Chronicoms about to launch an all-out invasion."
"And if we do, we have to take the enemy back with us," Mack added.
"I understand that. I do. But that decreases the chances of success a fair amount, something like 85%," Fitz insisted.
Immediately, everyone began to object. "This isn't some abstract or virtual world like the Framework," Coulson jumped in. "These people -- they've suffered enough."
As the others argued, Deke inspected the quantum bridge device. "This reduces you? Subatomic?" he asked. "Does it create an energy field to do it?"
"Yeah, it's like a bubble, for want of a better word," Fitz confirmed.
"No, no, bubble is a great word, because you can make it bigger," Deke replied. "If we use enough energy, we can bring the Chronicom ships back with us!" When Mack said the Zephyr couldn't generate that much power, Deke continued, "No, but 1983 New York City can!"
"Yeah, but we'd need something like 10,000 megawatts," Fitz calculated. "But someone would have to --"
"Stay behind and set it up and turn it on, yeah," Deke finished for him. "We have to break up the band."
Sousa quickly volunteered himself. "I'll stay," he announced, turning to Daisy and taking her hands. "I belong here. I've already been given the privilege of a second chance, of meeting all you fine people. It's only right. If the army taught me anything, it's that you can't be --"
Deke interrupted Sousa's speech by blowing a raspberry. "I'll stay," he cut in. "First of all, I'm the one with the scientific knowledge to be able to re-patch the power. Danny boy over here is still impressed by a light bulb."
"That's not accurate or nice," Sousa said softly.
"And secondly, it seems like you and Daisy have a real thing going, and I just want you to be happy," Deke added, locking eyes with Daisy. "And third, as long as you reconnect with Nana and then, you know, connect, then maybe you'll seem me again someday. And honestly, I'm kind of a rock god here anyway. Alright, people! No time to argue! I've already made up my mind, so let's get to it!"
As the team took off in the Zephyr, Deke set to work on rewiring the quantum bridge device to give them enough energy to get home with the Chronicoms in tow. He radioed in to let them know he was ready; Mack asked him to watch over his younger counterpart for him, and promised he'd never give up on friends. With that, the S.H.I.E.L.D. agents jumped to their original timeline, leaving Deke behind.
The resulting power surge caused a massive blackout, but his sacrifice was successful. In the wake of it all, Agent Brandon Gamble approached him and asked, "So, are you the new guy in charge now?"
Deke hesitated for a moment, taking in the request. "Yes," he replied with utmost conviction.
In the grand scheme of the show, Deke was a rather new addition to the S.H.I.E.L.D. family. He debuted in Season 5, as a member of the Lighthouse community that survived when Graviton tore the Earth apart. Begrudgingly at first, he helped the team navigate the post-apocalyptic world and the Kree the lorded over it. He was even willing to sacrifice himself to send them home, although the explosion that should have killed him actually sent him into the past with everyone else.
There, Deke had to adjust to a whole new world. He eventually reunited with S.H.I.E.L.D., where he learned of his surprising connection to the team. As it turned out, he was Fitz and Simmons' grandson, the result of a union between their daughter and a man who never appeared on screen. This brought him closer to the team than ever, and he stayed in their lives in order to connect with the only family he had left. Because of this, he ended up at Izel's temple in the Season 6 finale, which led him to join them in their final mission in Season 7.
The last few episode of Season 7 built up to Deke's sacrifice, starting with "The Totally Excellent Adventures of Mack and D," when he and Mack were stranded in the early 1980s. They spent just over a year there before the Zephyr reappeared, giving Deke time to establish a life. He made friends and founded a band called the Deke Squad; he also turned them into S.H.I.E.L.D. agents, at least to the best of his ability. From then on, he raved about his love for the 80s, even going so far as to jam to his own Deke Squad hits (all of which were stolen with his future knowledge, of course). As a result, his decision to stay behind makes sense, both for the story and the character.
Marvel's Agents of S.H.I.E.L.D. stars Ming-Na Wen, Chloe Bennet, Henry Simmons, Iain De Caestecker, Natalia Cordova-Buckley, Elizabeth Henstridge and Clark Gregg.