Carroll Spinney
Spinney performed Elmo back when he was simply known as Baby Monster. The first Muppeteer to perform Elmo by name was Brian Muehl. My favorite Muppeteer, Richard Hunt, also had a crack at the character but never liked Elmo:
"One day, frustrated with the role, Hunt came into the show's green room and literally tossed the puppet to Kevin Clash and asked what he could get out of it."
And the rest was Muppets history.