Katy Perry has transformed from young pop star to a wrinkled old lady for her latest music video.

The singer is unrecognisable, with lines, sagging skin and white hair as she plays a boozy retired Vegas dancer named Goldie in a clip from the video for Birthday.

"Have you ever heard that song The Lady Is A Tramp? That might be about me," Katy says in character as Goldie, who is clutching a glass of wine.

The short teaser clip also shows the star dressed up as a princess, an animal trainer and a male Jewish MC.

Katy, 29, also dons a clown outfit, complete with a curly green wig.

Speaking in a New York drawl, the clown says: "'I saw this thing on Craigslist to be a clown, make a few bucks at the weekend, I'm not a birthday party entertainer, I'm just trying to get some cash on the side... don't start drinking kids."

The characters are supposed to be the world's worst birthday party entertainers.

The singer will unveil the full video on April 24.

While she's been busy becoming other people, Katy recently showed she doesn't know as much about herself as one of her fans does.

The Dark Horse singer agreed to a game of trivia about herself against a fan during an appearance on Jimmy Kimmel Live! - and lost.

Katy and superfan Emily were quizzed about the star's career in the game - titled Who Knows Katy? - and the singer wasn't quick enough at hitting the buzzer to beat her opponent. Emily even answered more quickly than Katy when asked the name of the star's parents.