Jerry Nelson, the puppeteer and voice of Sesame Street's Count von Count, has died aged 78.
For more than 40 years, Nelson worked on numerous projects featuring Jim Henson's Muppets, including the TV series Fraggle Rock.
Nelson, who suffered from emphysema, died on Thursday in Cape Cod, Massachusetts.
A Sesame Workshop statement said he would be remembered for "the laughter he brought to children worldwide".
Nelson was born in Oklahoma, in the US, and raised in Washington DC.
He began puppeteering for Bil Baird, who produced and performed the puppetry sequence for The Lonely Goatherd in the film version of The Sound of Music.
Nelson's first job with the Muppets was The Jimmy Dean Show in 1965 - replacing Frank Oz as Rowlf the Dog's right hand.
He went on to work again with Henson on Sesame Street, going on to animate some of the long-running show's best-loved characters including Mr Snuffleupaguss.
But it was his mathematics-obsessed Count von Count, modelled on Bela Lugosi's interpretation of Count Dracula, with which he became most closely associated.
He continued to voice the character from 1972 until his death, though he ceased operating the puppet in 2004.
Nelson also performed many other characters on The Muppet Show, including Pigs in Space star Dr Julius Strangepork, the boomerang fish-throwing Lew Zealand, and Kermit the Frog's nephew Robin the Frog.
The Sesame Workshop said: "He will forever be in our hearts and remembered for the artistry in his puppetry, his music, and the laughter he brought to children worldwide through his portrayal of Count von Count, Herry Monster, Fat Blue, Sherlock Hemlock, the Amazing Mumford and many other beloved characters.
"We will miss his extraordinary spirit and the joy he brought to our Street."
Paying tribute on its Facebook page, Lisa Henson, CEO of the Jim Henson Company, added: "Jerry Nelson imbued all his characters with the same gentle, sweet whimsy and kindness that were a part of his own personality.
"He joined The Jim Henson Company in the earliest years, and his unique contributions to the worlds of Fraggles, Muppets, Sesame Street and so many others are, and will continue to be, unforgettable."