What happened to his career?

Yes, I AM talking about Biehn's performance, not just the character. He is the reason Reese had that radiance and intensity about him. He's the reason I bought everything Kyle Reese said and why I am able to suspend disbelief when I watch the film.

Contrasting that with say, Nick Stahl's John Connor from T3; nothing he said about Judgment Day affected me. This catastrophic event that the core of the story has forever revolved around seemed more like an after-thought most of the time. I never felt that sense of urgency that this mortifying event was coming like I did when Biehn created that imaginative vision of utter purgatory when he talked about it.

For me, not just anyone could've pulled that off.

https://www.quora.com/Whatever-happened-to-the-actor-who-played-The-Terminators-Kyle-Reese-Where-is-he-now

everybody in showbiz is easily replaceable

He's played some legendary characters from legendary movies. Maybe he turned down Weinstein, or some other satanic Hollywood elite?

https://www.hollywoodreporter.com/heat-vision/terminator-what-happened-star-michael-biehn-1228634

Essentially, wants to spend time with his family and isn't motivated by fame or money.

Sounds like a cool guy to share a beer with...

He reminds me of James Franciscus.

Both were rugged, handsome and in several big budget action films but never really hit that A-list leading man level.

Biehn’s other problem was being mostly an action film guy. I can’t remember seeing him in a traditional dramatic role.

He should have tried to get into an indie picture of some kind. Maybe he could have gained more dramatic credibility or some hipster value.

He was removed out of the Alien 3 script. That's the biggest problem. He never got a proper career boost in the 90s that would have kept him relevant.

https://www.reddit.com/r/movies/comments/1g0hlkl/comment/lr8w7u1/

People frequently blame the alcoholism, and that might have contributed, but frankly most of Hollywood is stuck on one vice or another, probably cocaine and very likely drinking.

Biehn didn't play the game. He wasn't attending parties and pulling favors, wasn't going to back rooms, etc. He was just a dude who went to work, did his job, pulled his weight, and went home, his job just so happened to be an actor. It's a big reason I think he and Cameron got along so well despite most actors seemingly not liking Cameron too much; Beihn went into the job expecting to work his ass off, give his input when appropriate, and otherwise not complain for the period he was at work. He had a mindset of that's what work was like and so Cameron early on appreciated his resilience and stuck him in some genuinely difficult work; Terminator, Aliens and The Abyss were each extremely physically and mentally demanding.

I think the falloff of his career was mostly Cameron's falloff as a director. Most his big films were with Cameron, with only a couple others which were either key bit roles (Planet Terror) or inexplicably took off (Tombstone) but for the most part the director which kept coming back to him was Cameron because, again, he didn't really play the game. Well, he didn't have much a role to play in the likes of T2 or True Lies, and certainly wasn't a fit for Titanic. And after that it was only Avatar, which Cameron wanted Biehn for the central antagonist role...but since he'd already cast Weaver he didn't want comparisons to be drawn to Aliens.