That was LetterMan. . .voiced by Gene Wilder and narrated by Joan Rivers. And yes, it was definitely on Electric Company. He would "rip the appropriate letter from his varsity sweater" to change things into more "convenient" things for him. For example, the "evil man" changed the "sun" into a giant "bun" by changing the "s" to a "b". . . . LetterMan took the "s" from his varsity sweater, changed it back to the sun, and the world was now again safe for Morgan Freeman to read to us.
My personal favorite EC cartoon was "TION, shun, shun, shun, shun. . . TION, shun, shun, shun, shun". . .
Come to think of it, didn't EC have episodes of SpiderMan? I seem to remember Spidey battling the Yeti. I think he set a bunch of snowcones on the ground, and the Yeti (yearning for all things cold) sat on them one at a time. . .giving Spidey plenty of time to escape, save the hostages, write a novel, etc. . . .