It is, easily, Filmation's most successful series in the near quarter-century the company was operating. After all, Fat Albert & The Cosby Kids lasted for about half of that time.
To be fair, CBS nearly didn't get the series. An early pilot showcasing Weird Harold had aired on NBC, produced while series creator-star-co-executive producer Bill Cosby had his first self-titled sitcom on the air, I believe. However, Weird Harold was made at a different animation studio, and so Filmation landed a gold mine by signing on with Cosby.
Fat Albert bowed in 1972, but for the entirety of its CBS run, was left to air at lunch time (12 pm ET), which historically means bad news for a lot of children's shows. Despite a 12 year run at CBS, there weren't that many episodes made, just enough to get the series into syndication in 1984, which would be Fat Albert's final season, as Cosby moved back to primetime and NBC, and, of course, the rest is history.
Cosby had left the original Electric Company to focus on Fat Albert, but, then, he also sold tons of Jell-O through commercials. Toward the end of the run, Cosby would add a superhero satire, Brown Hornet, as a show-within-a-show that the gang would watch, and would take over the Picturepages segment of Captain Kangaroo. Can you imagine if Cosby & Danny Kaye, America's other ambassador to children, ever did anything together?
Following is an open-close from the mid-70's: