Toei’s answer to the American Saturday morning imports that were quite popular on Japanese television in the 1960s. You can see how how creator Yasuji Mori’s character designs were clearly influenced by Ed Benedict, the designer on many early Hanna-Barbera cartoons. Despite the limited animation necessary for turning out episodes on a weekly basis, I’d say the actual style of the show’s humor has more in common with classic American theatrical cartoons, albeit with a uniquely Japanese flavor added as well. Also worth mentioning that Hayao Miyazaki was a key animator, and Isao Takahata directed the hilarious opening title sequence.
Charles Brubaker wrote a good article about this show on the always entertaining and enlightening Cartoon Research website. You can read that article here. I also adopted his romanizations for some of the character names, since I liked them better than the ones I had originally chosen.