Since the end-credits stinger in X-Men: Apocalypse, we've been waiting for official word on when and how Nathaniel Essex—aka Mr. Sinister—was going to make his way in the X-Men cinematic universe. Well, it looks like it wasn't long term set-up (like everything else in that film was), but rather the kind of set-up that's going to have a pretty immediate payoff.
According to Cinema Blend, director Bryan Singer revealed during the commentary track for X-Men: Apocalypse that the Weapon X vile being put into the Essex Corporation briefcase is direct set-up for the next Wolverine solo adventure, tentatively titled Weapon X. Considering that film is due in theaters in seven months, it's nice to have any tiny bit of information about it beyond the fact that Hugh Jackman's beard is back.
As far as casting goes, the best guess floating around right now is that Richard E. Grant, star of Withnail & I (watch it, you won't regret it), is the most likely candidate to be playing Essex. He and Eriq "Soul Glo" La Salle are both appearing in undisclosed roles in the film, and either of them could be playing Essex, I suppose, but I give Grant the edge since his role is rumored to be a "mad scientist," and knowing his track record, he'll likely kill it in this role. Of course, we'll keep you up to date with the latest information as it comes in!