It was kind of pathetic, really. The series started with Bimbo having the only billing. In fact, Betty didn't even get her name until 1931. But soon it was "Bimbo Assisted by Betty Boop," and then "Bimbo and Betty Boop," evolving (or devolving, depending on whose side you're on) to "Betty Boop and Bimbo." And that wasn't the end. Soon it was "Betty Boop Assisted by Bimbo," and finally "Betty Boop Assisted by Bimbo and Koko." Koko was a clown who appeared without fanfare or apparent purpose except to help pull Betty out of trouble and get himself and Bimbo into trouble, generally at the same time. Yes, Bimbo was not only second fiddle; now he had to share what little limelight he had with some clown. You kinda gotta feel sorry for ol' Bimbo.
Sometime in 1932, as Betty became more and more popular, she evolved (or devolved, depending on your point of view) into a human. Her dog's snout turned into a girl's nose, and her floppy ears became large hoop earrings. Oddly, even though she wasn't a dog anymore, and Bimbo still was, there were occasional cartoons where there was a definite romantic inclination, at least implied. Maybe just a tad creepy, if you let yourself think about it.
As more conservative elements gained control over the entertainment world, the surrealistic, almost hallucinogenic, plots and sexual innuendo were toned down considerably. The hapless Bimbo and sidekick Koko just sort of faded away. As her dress grew longer, and her actions less outrageous and overtly sexy, her popularity waned, kind of like Angelina Jolie. The last Betty Boop cartoon was shown in 1939. While she had some cameos in the eighties, and is still occasionally seen on lunchboxes and the like, she never recaptured her former stardom. But cartoon characters don't need facelifts or Botox. They're young forever, and perhaps someday Betty's star will shine once again.
About the Author: Matt Roberts is an essentially harmless and only slightly psychotic geek who runs a website devoted to all things yesterday. Said site is where you may be able to catch a glimpse of his skewed perception of the known universe, and there's some fun stuff there too. He has neither life nor hobbies. And before you ask: No, he's probably not that Matt Roberts. It's a pretty common name, actually.