Celebrity guest stars on 'Sesame Street'

Nicole Kidman - Nicole Kidman appears in a 'Sesame Street' sketch to discuss the word "stubborn" with Oscar the Grouch".

Oprah Winfrey - On a 'Sesame Street' episode, Oprah Winfrey parodies herself by providing the voice for a cartoon letter "O,"

Sia - The singer joins a few of the 'Sesame Street' characters to sing along with them. The name of the tune is 'S is for Songs with Sia.'

Mark Ruffalo - The actor appears in 'Sesame Street' in a sketch with Murray, in which they enthusiastically discuss the meaning behind the word "empathy."

Alicia Keys - The singer appears on 'Sesame Street' alongside Elmo in a sketch where she performs a slightly altered version of her hit song 'Fallin'.'

Sarah Jessica Parker - SJP appeared on 'Sesame Street' to talk all about the word "pair" with Elmo. They look at pairs of various things together, including ice skates.

Blake Lively - The actress appeared on 'Sesame Street' to share memories of the show and to pass her congratulations on 50 years by saying "Happy Anniversary!"

Mila Kunis - The actress has appeared in a couple of 'Sesame Street' sketches.

David Beckham - The retired soccer star appeared on 'Sesame Street' to discuss the meaning of the word "persistent" with Elmo.

Mario Lopez - In 2012, the actor and host appeared on 'Sesame Street' in a sketch where he starts a rumor that the Cookie Monster has become the Veggie Monste

Natalie Portman - The actress joins Elmo on a 'Sesame Street' sketch to play a game of "Princess and Elephant." 

Ellen DeGeneres - The comedian has both appeared on 'Sesame Street' and had the show come to her! Indeed, the character Oscar the Grouch appeared on her talk show.

Claire Danes - The actress appears on 'Sesame Street' alongside the Cookie Monster to have a serious talk about diagrams. But the Cookie Monster has other ideas!

Bruno Mars - The singer joined some 'Sesame Street' characters to sing a song called 'Don't Give Up.' The sketch has over 100 million views on YouTube!

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