Elmo has been performed, since 1985, by Kevin Clash. The character is supposed to be somewhere around 5 years old, and speaks of himself in the third person.
A popular doll called the Tickle Me Elmo was manufactured in his likeness, and became the must have toy during Christmas in the 1996.
Elmo also routinely appeared on the Rosie O'Donnell show, and starred in a full length motion picture entitled Elmo in Grouchland.
ELMO, Electronic Mail Operator, is also a feature-rich, highly configurable and fast mail client for UNIX-like operating systems. You could call it a Mail User Agent, but it offers much more than traditional MUA's: