Actor Josh Duhamel had a major co-starring role in the original live-action Transformers movie, and he came back to mix things with the Autobots and Decepticons for the two subsequent sequels. However, when the fourth installment (Transformers: Age of Extinction) opted to "soft reboot" the series and not include any of the original human cast, Duhamel's military man Lennox appeared to be gone from the franchise for good.
Things have since changed and now Lennox is returning for the next installment in the series, in the form of 2017's Transformers: The Last Knight. On the set of The Last Knight, Duhamel both explained how that worked out and touched on what his Transformers character was up to during the events of Age of Extinction - as well as his complicated relationship with another human character in The Last Knight, Santos (Santiago Cabrera).
Duhamel, when asked about his return to the Transformers franchise for The Last Knight's set, agreed that Age of Extinction was a soft reboot of the series:
Yeah, it was definitely a reboot. And it was a little sad because I’d done the first three. But I was fine with it. And then they asked me to come back. And I was like, “I’d love to do it again.” It feels like, and this is a testament to Michael [Bay], 80% of this crew was there from the beginning, from the very first movie. So you see all these faces you worked with almost 10 years ago. Most of this crew is back. People can say what they want about him, but these people love him. They hate him at times, but they also love him.
In the original Transformers trilogy, the Autobots were eventually accepted as allies of the human race (and the U.S. Military in particular) and Duhamel's Captain William Lennox fought alongside them; both during his service with the U.S. Army in the first two films and as a member of the joint human/Autobot NEST task force in Transformers: Dark of The Moon. However, post-Age of Extinction, the Autobots and Decepticons alike are fugitives from a paranoid humanity that hates and fears them. Thus, Lennox has a for-now unclear relationship with the Transformers Reaction Force (TRF): a paramilitary unit assigned to hunt and destroy all alien robots.
Duhamel had the following to offer, with regard to Lennox' absence during the events of Age of Extinction - as well as the character's relationship with Santiago Cabrera's ruthless TRF operator, Santos, in The Last Knight:
Well, the last one, to sort of justify it to myself, there was no military element. Therefore they didn’t need me. I think it was probably they just didn’t want me (laughs). But this time there is definitely a military element here and what brings me back is, there’s a question as to who I’m working for. Am I with the US military, the Army, or am I working with a group that’s trying to eradicate all Transformers? Not just Decepticons, but all of them. There’s a bit of a struggle between myself and Santiago Cabrera, and then we’re also working against [Mark] Wahlberg’s character in this. Because he’s definitely working with the Autobots. It’s just a lot of big fun movie s--t that we get to do. And what brought me back personally is the fact that you get to do stuff that you don’t get to do anywhere else. Michael [Bay] does stuff bigger than anybody I’ve ever worked with for sure. I’m a tiny cog in this machine. I get to see some really cool s--t.
As for the NEST, Duhamel confirmed that the group is not a part of the story in The Last Knight:
NEST is not in this. There’s a different group. NEST was a group where we worked with the Autobots. It’s so crazy to talk about. It’s all based on a true story by the way. But this group, there’s sort of a worldwide coalition to eradicate all of them. They’re all bad. And a few of us know better, but that’s sort of it.
