Does This Remind You of Anything?: The parallels between Kimba and The Lion King are many, even if the latter does officially base its plot on "Hamlet". Helped by, among other things, both properties making similar design goofs (black tips on the main character's ears, which in reality is uncommon; Dan'l and Rafiki sharing nearly identical story purposes and both incorrectly labelled as baboons – they are mandrills), both properties' villains' tendency to pal around with hyenas, early Lion King production sketches that showed Simba colored white (to which a producer is said to have remarked, "Not even our lawyers are that good."), rumors that Disney had been trying to get the Kimba rights from Japan during the court battles over Mushi Pro's IP, and Matthew Broderick admitting in an early interview that he thought he was signing up for a "remake of that cartoon [he] watched as a kid".
Upon seeing The Lion King in theatres, Kimba's voice actress Billie Lou Watt was quite vocal about the similarities to the show she'd recorded years earlier. She didn't use the words "ripoff" or "plagiarism" to describe the Disney film, but did imply those terms. Tezuka fans have since used them openly.
In 1995, after The Lion King premiered in Japanese theatres, Tezuka's widow was reportedly asked if she would consider levelling infringement charges against Disney. She said no, reminding the questioner that her late husband was profoundly influenced by Walt Disney and had tremendous respect for him; she concluded that he would never think of suing Disney's company, so neither would she.
Executive Meddling: Tezuka wanted to make an epic series exploring the meaning of family and sacrifice. NBC wanted a kid's show. Ironically, this may actually have been a good thing as the compromise they worked out made the story much less depressing and one of the most popular incarnations.
NBC asked that the series be cut from Tezuka's planned 78 episodes to 52, at the insistence of local NBC affiliates who demanded an easy number for programming purposes (one episode every Saturday for a full year). Tezuka agreed. NBC further required that, instead of Kimba maturing over the course of the series as Tezuka wanted, he stay a cub for the entire run and the show have Negative Continuity – this was also an order from local stations in the US, who didn't want to have to show episodes in order (and in fact, they didn't). Tezuka agreed, but then promptly had his animators do whatever they could to subtly undermine NBC's dictates.
Being a Fred Ladd production, there's a lot of vocal crossover between this and other 60's dubs. Kimba for instance is Astro Boy and we get such gems as Mr. Pompous from another universe, playing Mr. Pompous from this one.
Dan Green providing Leo's voice in the movie dub bought a whole 'nother level of enjoyment to the table. To add to the incessant giggling, he's also apparently married to April O'Neill in the film, as Veronica Taylor plays Lya.
Keep Circulating the Tapes: Operative until the late 90's. NBC's license for the original series lapsed in 1978, shortly after Tezuka's Mushi Pro studio went under. So for nearly two decades, the only way to see any of the series was through very early awful-quality VHS tapes, and even then it was just a handful of the 52 episodes produced. The rights to this series – along with the rest of Mushi's properites – were tied up in court for pretty much the entirety of the 80's. Through what can best be described as pure luck, Right Stuf – which already had the rights to Astro Boy – managed to license this series and release it in its entirety.
This still applies to everything else Kimba-related, though. The movie was an exception, but has since gone out of print due to its distributor falling on hard times and letting the license expire.
Money, Dear Boy: This explains why Osamu Tezuka agreed to so many of NBC's Animation Age Ghetto demands. Astro Boy was a big hit in the US and NBC wanted Tezuka to make them another show, this time in color. However, Japan hadn't made the switchover to color broadcasts yet. Mushi Pro wasn't equipped to produce anything in color and didn't have the resources to convert the studio, so NBC said they would pay to convert Mushi to color production, so long as they had say over Kimba. This was the result.
No Export for You: The original manga has yet to see a English-language release; the unfortunate representation of African Natives in this series – and Tezuka's drawings of coloured people in general – seems to be a significant barrier for publishers.