He could be that character that was immortal. Prhaps in one of his past persona's he was a brilliant detective or something.

Talk about boldly going...

The most recent Nerdist Podcast was an interview with Brent Spiner, and apparently Cumberbatch approached Spiner & Patrick Stewart while they were eating in a nice restaurant. The long of the short of it was, he insisted on speaking to Stewart right then and there, then said "I just signed on to be in the next Star Trek movie. Will that damage my career?"

To which Spiner immediately swore that he'd never find work again.

That's funny when you consider how much we saw each actor post TNG - Stewart (3 x-men movies +) and Spiner (... I got nothing)

He went on to do Broadway roles, he had a small role in Independence Day as a crazy scientist, and he currently is starring in a very funny web series that I just created a new thread for.

ID4 was a small part 15 years ago. The rest of those I (and probably most people) have never even heard of much less seen - as opposed to the X-Men franchise which virtually everyone has an opinion on.

I have long found Brent Spiner's disappearance from TV puzzling. If I were a TV producer and I wanted to do yet another crime drama and I wanted "quirky labcoat guy" in my cast (and which crime drama doesn't have that), Brent Spiner would be on my short list.
It makes me wonder if he has had offers like that and just never taken any of them.
If not that, I would expect to see him guest starring on every TV show ever created.
Actually, it would be cool for him to create a wandering homeless vagabond character and have him do small guest roles on multiple shows (probably on the same network.)

I still want Space Lincoln.

or Space Giant Hand

Brent Spiner also had a cameo on The Big Bang Theory playing the part he was born to play: Brent Spiner the guy who played Data.

Will Wheaton had a quick cameo in Star Trek as one of Nero's Romulan buddies. No reason Spiner couldn't play a non-Data/Soong character. Jeffrey Combs played three or four roles on DS9.