Before Benedict Cumberbatch became Marvel's Doctor Strange, the name that was being bandied about in regards to the character was Joaquin Phoenix. Now, the actor speaks out about why he didn't become the Sorcerer Supreme. While Phoenix is not usually associated with movies that fall into the "blockbuster" category, he says he doesn't have a problem with those sorts of films, but it does sound like the two sides reached some sort of impasse in negotiations. According to Phoenix...
I think they make some great, fun movies. There's nothing wrong... I'm not a fucking, like, cinephile. I'm not a snob and I'm totally fine with... I enjoy those movies sometimes, and I think they keep the fucking industry going in some ways, so I don't have a problem with it at all. I think that everybody was, is... I'm trying to figure out how to say this most diplomatically, okay... I think everybody was really happy with how things turned out. All parties were satisfied.
Clearly, there were talks between Joaquin Phoenix and Marvel that broke down over something, but Phoenix isn't looking to throw anybody under the bus and looks for the political way to exit the question from Little White Lies. For what it's worth, he says that all parties were satisfied in the end, which seems to imply that Phoenix doesn't feel like he missed out on the opportunity to play Doctor Strange, and he thinks Marvel was also ultimately happy that he didn't take the part. It's unclear if he thinks Marvel was happy after Phoenix decided to abandon the project or just after the movie was successful with Benedict Cumberbatch.
Back in the lead up to the production of Doctor Strange it really seemed like we were going to get Joaquin Phoenix in the title role. At one point, he was described as being in "final negotiations" and, while we don't know how true that was, it does appear that there was real interest from both sides. We've never heard anything specific that has given us any indication as to why it didn't happen. Clearly, Marvel wanted him at one point, and Phoenix does say he was interested. He certainly didn't have an issue appearing in a big budget comic book movie. Perhaps the two sides both realized that, as great as the idea might have seemed on paper, it just wasn't going to work out well in practice, and so they walked away.
Joaquin Phoenix as Doctor Strange will likely be one of the great "what if" scenarios of recent movie history. It certainly would have been a very different movie with him in the lead and I'll always wonder what that would have looked like.