The Tortoise -- or "the Turtle", as he's sometimes known to sports fans -- is one of the main characters from the classic Aesop fable "The Tortoise and the Hare".
Kermit the Frog broadcasts from the scene of the great race between the Tortoise and the Hare in a "Sesame Street Sports" sketch from a 1971 episode of Sesame Street. When the race begins, the Hare offers to give the Tortoise a head start -- but when Kermit rushes to the finish line to see the results, the Frog is inadvertently crowned the winner of the race.
In a second "Sesame Street News Flash" sketch, the Hare challenges the Tortoise to a rematch. This time, the Tortoise comes equipped with a jet-pack.
The tortoise puppet appeared in a sketch with Waiter Grover where he worked at O'Brien's Restaurant. The Tortoise, referred to as Tony, delivered the "slow food" for those not interested in Grover's take on "fast food".
In the first sketch, the Tortoise was made out of the regular Green Anything Muppet, and featured that puppet's distinctive cone-shaped head. The Tortoise in the second sketch had a more turtle-y design, with no cone-head.
- The Sesame Street Dictionary (1980)