In 1966, a producer named Steve Krantz and an animation studio called Grantray-Lawrence produced 65 half-hours of The Marvel Super-Heroes — a syndicated cartoon series featuring Captain America, The Hulk, The Sub-Mariner, Iron Man and Thor. Years later when I asked Stan Lee, "Did anyone like that show?" his reply was, "Yeah, Steve Krantz. He got all the money." Stan believed that Marvel publisher Martin Goodman had made a rotten deal in order to get his characters on TV in the hopes that (a) a flood of merchandising deals would occur and (b) it would make Marvel look more successful because Goodman was then hoping to sell the company — which he did just a few years later.
The stories and artwork were mostly adapted from the actual comic books, infuriating most of the artists who had drawn and plotted those stories for low comic book rates and now saw their work used on television without a cent of additional compensation. It and a subsequent Spider-Man TV cartoon done under the same deal seems to have been among the main reasons why Steve Ditko left Marvel.
And the animation wasn't very good. When the cartoons aired in Los Angeles, they were initially on a kids' show called Shrimpenstein and the host would introduce they by saying things like "And now, here's another one of those cartoons where nothing ever moves" or "and now, another Marvel mediocrity." (I have been accused of making those lines up but ask anyone who watched Shrimpenstein on Channel 9 back then. They will confirm.)
The voice work was variable — done on the cheap in Canada — but the stories were pretty good. And for comic book experts like myself, it was kinda fun to watch the show and identify the drawings used. If the Hulk was standing in profile, that might be a Ditko drawing and then he'd turn full face and that would be a Jack Kirby drawing and then he'd turn the other way into a Bob Powell drawing.
And you know what else wasn't bad? The music. The cartoons had catchy theme songs written and supervised by a New York composer named Jacques "Jack" Urbont.
There is no good release of these cartoons on home video but bootlegs abound. If you've never seen these cartoons, you can watch some prints of varying quality on this page. Also, someone has come across good recordings of the opening and closing themes and Disney has recently released a vinyl (vinyl!) record of them which may interest you if you have something to play it on. Or you can listen to those recordings in these two online videos…