Disguised beneath a frock of bright yellow feathers and an orange bill, the Sesame Street puppeteer was the heart and soul behind Big Bird, as well as playing Oscar the Grouch since the show's premiere almost 50 years ago.

Now, at the age of 84, Spinney has told the New York Times he is retiring from Sesame Street after nearly half a century playing some of the show's most iconic characters.

Come Thursday, Spinney will enter the Sesame Street studios in Astoria, Queens for the last time before leaving the roles behind forever.

"Before I came to Sesame Street, I didn't feel like what I was doing was very important. Big Bird helped me find my purpose," Spinney said in a statement.

"Even as I step down from my roles, I feel I will always be Big Bird. And even Oscar, once in a while! They have given me great joy, led me to my true calling - and my wonderful wife! - and created a lifetime of memories that I will cherish forever."

Spinney said the physical requirements for the show have become more and more difficult in recent years.

Starting in 2015, he transitioned out of the Big Bird suit after developing a balance problem in the costume and has since been providing only voices for the character.

His final voice recordings will be used during the upcoming 50th anniversary next year on HBO.

Taking over the roles of Big Bird and Oscar the Grouch are longtime puppeteers Matt Vogel, who plays Kermit the Frog, and Eric Jacobson, who plays Miss Piggy.

Australian Associated Press