Answer: Producers and T.E.C.

Nobody bit on my question last week on the significant connection between the The Producers (original movie version) and the children's television show The Electric Company. So... the answer is:

One of the recurring TEC sketches was called The Adventures of Letterman (no relation to Dave). In this animated segment, the title character, a superhero wearing a varsity sweater, would foiled the mischief of the evil Spellbinder by tearing the letter off his chest to fix words the villain had corrupted. Spellbinder and Letterman were voiced by Zero Mostel and Gene Wilder respectively, the two leads in The Producers! Since this TEC sketch debuted only a few years after The Producers, the voice casting was surely deliberately meant to evoke that great comedic pairing.

Faster than a rolling 'O'
Stronger than silent 'E'
Able to leap capital 'T' in a single bound!
It's a word, it’s a plan...it's Letterman!