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Twenty-one puppets created by Jim Henson for The Muppet Show, Sesame Street and Fraggle Rock have been donated to the Museum of American History in Washington.

Miss Piggy has now joined her on-screen paramour Kermit the Frog in the Smithsonian Institution's collection.

Cookie Monster, Bert, Ernie, Elmo and Fozzie Bear were also "inducted" during a special ceremony on Tuesday.

The event took place on what would have been Henson's 77th birthday.

Jim Henson died in 1990, while his wife and collaborator Jane died in April this year.

Their daughter Cheryl, who is president of the Jim Henson Foundation, said she was "so happy to have [her] father's work be part of the cultural heritage of this country".

"When you look at these different characters, you can hear their voices," she said. "They are like living beings."

The fame-seeking Miss Piggy will be on view within the museum's American Stories exhibition, which starts in March 2014.

Several other Muppets and Sesame Street characters will be part of a broader puppetry display that will open this November.

"The Muppets are very much a touchstone to my childhood," said museum director John Gray.

He called comedy and variety programme The Muppet Show, which ran from 1976 to 1981, "the best example of American vaudeville".

The donation also includes Scooter, the Swedish Chef, Grover and Count Von Count, as well as Boober Fraggle and Travelling Matt from Fraggle Rock.

Many of the puppets show the characters as they were first constructed.

These include Rowlf, a scruffy brown dog created for a dog food commercial in the early 1960s who later joined The Muppet Show as a pianist.

"Kermit was Jim's alter-ego, but Rowlf was Jim's alter-ego without the ambition," said Karen Falk, an archivist with The Henson Corporation.

"He was Jim on the weekend, Jim in a hammock."

The museum is already home to Oscar the Grouch, Kermit and the cast of Henson's early TV show Sam and Friends.