Robert Downey Jr joins Twitter

'Iron Man' star Robert Downey Jr has made an account on micro-blogging site Twitter.

After joining the site on April 11, the 49-year-old actor posted a photo of himself holding a sign bearing his name, reported E!Online.

"Talk to me, Twitter. You know who I am," Downey said in his first tweet.

The actor said he was having trouble in putting his thought in limited words.

"Loving all the love, folks. It's been a blast. Though can somebody please explain how anyone can keep their thoughts to 140 characters," he tweeted.