He was born in Dodge City, a fighting town, that's what should be remembered about Dennis Hopper. While still a youngster and still in Kansas, he studied art with Thomas Hart Benton.
He died in Venice, California, where he long made a reputation for himself as one of the genuine American hipsters. A legendary photographer to many. An actor in a ton of crummy films and a handful of reputable ones where without his presence, no film. Or at least not the little bit of cinema masterpiece that came with it. He just showed up in the oddest places with the oddest decisions and there is something memorable about that savvy lust and defeat.
Supposedly John Wayne chased him with a loaded rifle on the set for True Grit. Probably deserved it.
He starred in two James Dean films, and that's one shy of how many films James Dean ever starred in.
For fun, check his early acting out in the small film called Night Tide (1961). I've never forgotten it.
He probably was an asshole. I've been called one. So have you.
There's no one to replace him. Just look around.