Celebs flocked in droves to celebrate the Sherlock Holmes star's half-century birthday on Saturday night.

Among the revelers were Orlando Bloom, Jason Bateman, Dustin Hoffman, Justin Theroux and Jennifer Aniston,Tobey Maguire and Jen Meyer, Edward Norton, Reese Witherspoon, Jack Osbourne, Katie Holmes, and Gwen Stefani and Gavin Rossdale. Fellow Avengers stars Samuel L. Jackson and Jeremy Renner were also on the guest list.

A few minutes after 6:30, the birthday boy himself arrived with wife Susan. As he entered the party -- through a tunnel of smoke, natch -- speakers blared "It's My Party."

There was live music, too -- from none other than Steely Dan and Duran Duran, the latter of which played a 45-minute set including hits like "Come Undone," "Rio," and "Ordinary World." Toward the end of the bash, everyone joined together in singing "Happy Birthday" to Downey Jr.

Courtesy Us Magazine