Its not surprising you never saw the series since it like, came out in the 60's? And the manga was the 50's?
That page is full of TRUTHS. Disney animators ripped/homaged an anime source, while the execs in charge may have been less aware. (Or at the very least, have to publicly pretend they had no idea.) It may be off on some of the behind the scenes stuff, but it all sounds accurate, since the visuals and scenes that are the same are, well… visuals and scenes that are the same
They do that.
A lot.
See also Rescuers Down Under/Nausicca flying sequences, Great Mouse Detective/Castle of Cagliostro clock tower sequence, and Atlantis/Nadia.
But yeah. Lion King has a TON of similarities to Kimba in scenes and visuals. Right down to them both having black spots on the ears, which isn't really a typical lion trait. That page lists a pretty good chunk of them. Hell, the earliest production art even had Simba as a white lion.
I mean, they had a mandrill shaman, a colorful bird advisor, some hyenas, evil scarred black maned uncle named Claw, the stampede, the father in the sky after the little lion runs away from home... the biggest difference actually is that Kimba/Jungle Emperor Leo had humans in it, and being a series, a lot more to it in terms of themes and well... episodes, and followed Kimba all the way to his adulthood, having children, and then his death. The actual stories were pretty radically different, but a lot of the SCENES were very similar.
Really. Just watch the first... 5 minutes of the movie and pretend Circle of Life is playing.
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Matthew Broderick even thought he was working on a Kimba remake.
Another fun fact. Kimba's name originally WAS Simba, but there were copyright issues with a sports drink at the time or something. (Well, its Leo in the Japanese regardless.)