Mr. Bates' work appeared on Sesame Street beginning in the first season. His name was mentioned in Episode 0261 when Oscar and the kids watched him write an E, and in Episode 0300, when Susan spotted him making a Q. He was also mentioned by David in Episode 0536, during a game of "follow the leader".
The actual skywriting in the original segments was done by Cecil Coffrin of Sky Advertising Corporation. Beginning in season 11 of the show, he began to make the occasional appearance out of the skies and on the street, portrayed by Muppet performer Brian Muehl. In these appearances, he would drop from the sky and write on-screen (with the use of a telestrator) while imitating the sounds of his airplane, then somehow rising back up into the sky. In season 12, he was joined by Dominique, an Anything Muppet who served as his driver (using a motorcycle).
Alphabet Bates made an illustrated appearance in the 1983 book Everyone Makes Mistakes. He appears in the animated adaption of the story for Three Sesame Street Stories, where he's heard speaking in a French accent.