Was "Birdman" and/or "Riggan Thomas" written for Michael Keaton?

Question

Some elements of Birdman seem custom-fit to the actor Michael Keaton:

1. He plays Riggan Thomas, an actor who is about 25 years removed from a blockbuster role as a superhero, just like Michael Keaton is about 25 years removed from his role as Batman
2. "Riggan Thomas" has same syllable count and similar intonation as "Michael Keaton"
3. The name "Batman" is obviously similar to "Birdman," the outfits look nearly identical, and the voice of Birdman sounds similar to the voice of Keaton's Batman
4. Keaton turned down a third Batman movie, like Riggan turned down a fourth Birdman movie

However, other elements don't really fit:

1. Riggan seems to be defined by his Birdman role in the way Christopher Reeve was defined by Superman or Roger Moore by James Bond -- but Michael Keaton was never really defined by the Batman role: he's just as popular for roles like Beetlejuice and Mr. Mom
2. Batman 3 was not a commercial success, and Batman 4 was a disaster, so Keaton's exit after the second sequel seems like it was a smart career move, not something he would regret like Riggan regrets negging Birdman 3
3. Keaton has never tried to re-invent himself along the lines of writing, directing and starring in his own Broadway play, like Riggan does

With all this in mind, was "Birdman" and/or its "Riggan Thomas" character written specifically for Michael Keaton?

Answer 1

It does not appear to have been so. Reading Kirsten Acuna's Business Insider article, It Took Michael Keaton About 27 Seconds To Decide To Be In 'Birdman':

During a panel at New York Comic Con for the film, Keaton shared the story of how he was cast in director Alejandro González Iñárritu's movie about a washed-up actor, Riggan Thomson (Keaton), hoping to rejuvenate his career with a Broadway play.

Keaton said he first learned about "Birdman" while filming another movie, which he flew home in the middle of shooting to discuss.

"I got a call saying, 'Alejandro was making a movie,'" said Keaton. "I was working on a movie and they said, 'well, unfortunately, you probably can't fly home because you're in the middle of making this movie' and when his name was mentioned, I said, 'Well, maybe I should find a way to fly home because, like I'm sure Edward [Norton], I'm a big, big fan of his movies."

The actor said it took him less than 30 seconds to decide to star in the movie after dinner with Iñárritu who has made movies including "Babel" and "21 Grams."

"So, it was that simple. I flew home and they wouldn't ... they couldn't tell me what it was about and now that I've done the movie I understand why they couldn't explain it because I'm not sure what happened," he said.

"I went and had a dinner with him [Iñárritu] and it was very pleasant and very interesting," Keaton said. "If you've ever spoken with him, you'd know why. He's just a very interesting, extremely passionate guy which is contagious. At the end of the evening he said, 'Well, here. Read this.' It took me about, I don't know, 27 seconds to decide, 'Yeah, I want to do this.'"

If it had been specifically 'written with Keaton in mind', he would have been actively courted. If this article (and Keaton himself) is to be believed, he dined with Iñárritu and only then was given the script to read and accepted it. Had it been written 'for him', it seems more likely that they'd have contacted Keaton (or his agent) directly, and he'd have been in on it from the beginning.