I assume he taught combinatorics.
Somehow I never connected for a while that the characters on Sesame Street were “official” Muppets as in the Muppet Show.
A few decades after Roosevelt Franklin, there was Kingston Livingston III:
They were (and are) “official” Muppets, though with a few exceptions (primarily Kermit, who predated Sesame Street, and who was Jim Henson’s alter ego), the Sesame Street Muppets are exclusively used for that show (and its spin-offs), and don’t cross over with other Muppet productions, like The Muppet Show, save for very occasional cameos, such as Big Bird’s appearance in The Muppet Movie.
Originally, Henson retained ownership of the Muppets which he and his studio created for Sesame Street, but the rights to those Muppets (again, with the exception of Kermit) have been owned by Sesame Workshop since 2001.
According to the Muppet Wiki, he said he was “professor of counting from one to ten at the Institute of Technology at Moldavia.”
There’s also Elijah and Wesley, introduced earlier this year:
I always thought of Grover as being “ethnic” due to his accent which differs from General or Standard American English pronunciation.
Grover is a Monster-American. 
Heh, Cookie Monster, as well, for that matter.
I remember the day I realized that Grover and Yoda have basically the same voice.
Was Oscar the Grouch black or was that literally just the SNL parody of Sesame Street?
Also Herry:
He wasn’t intended to be black, I don’t believe. Oscar’s Muppeteer, Carrol Spinney, stated that he got his inspiration for Oscar’s voice from a NYC cab driver who drove him to the studio; Jim Henson, along with writer Jon Stone, are said to have based Oscar’s personality on Oscar Karp, the “magnificently rude” owner of the restaurant Oscar’s Salt of the Sea.
But, that said, as noted in the Wikipedia article on Oscar: