Dr. Sheldon Cooper is about to meet Doc Brown.

It was announced on Wednesday that CBS’ The Big Bang Theory has tapped Back to the Future funnyman Christopher Lloyd to guest-star in the Thursday, Dec. 1, episode.

In touting the casting, the series’ executive producers said that they were “so excited” to be working with the veteran actor, whose small-screen credits include appearances on everything from Cheers to Chuck, of course his 1978-83 stint as Taxi’s Reverend Jim Ignatowski, and an upcoming visit to Syfy’s 12 Monkeys.

The EPs added that, although they weren’t revealing exactly who he’d be playing — or whether time travel would be involved — “We think we’ve created a fun part that fans will really enjoy.”

Who do you imagine Lloyd will be playing? Maybe they’ve found a way to give him a scene or two with fellow Taxi alum Judd Hirsch (aka Leonard’s father)? Hit the comments with your theories and/or hopes.