Joe Pesci was approached for the role of Banzai, but turned down the offer due to scheduling conflicts with A Bronx Tale.
Tommy Chong was originally going to be the voice for Shenzi, reuniting him with his comedy partner Cheech Marin and turning the hyenas into a three man band. However, both men were not on speaking terms at the time. Whoopi Goldberg was cast in his place and the character was changed to a female once the writers discovered that hyenas are matriarchal.
Tim Rice originally wanted Rik Mayall and Adrian Edmondson to voice either Timon and Pumbaa or the hyenas, as he was big fan of Bottom. They were both considered to voice Zazu.
The story was originally known as King of the Jungle and the plot was far Darker and Edgier. It had a few variations. In early scripts the Pridelanders were called the Ndona pride. Scar was a rogue in at least one draft, but it was decided to make him Mufasa's brother as it made the film emotionally investing. One script was to be themed around a war between two prides of lions. Scar was the leader of the "Mbala" pride, with Mufasa leading the "Ndona" pride. There was also a group of hyenas, led by Banagi (who later became Shenzi), who would have served as secondary antagonists. Kwashi was a baboon similar to Rafiki, though not as wacky. Noticeably it was much more violent and incest filled than the final product (a similar concept to this, albeit Lighter and Softer, was in the first Direct to Video movie).
Richard Curtis and Ben Elton were approached to write the film, but both turned it down as they were busy with projects of their own.
Multiple characters have ended up scrapped for the final version of the first film:
Nala had a younger brother named Mheetu who played an important role. He was created as a character for Nala to protect from the hyenas and Scar. Mheetu was the one who was lured into the gorge, not Simba. Simba tried to save him but failed, so Mufasa saved them. Contary to popular belief, Mheetu was tan like most cubs rather than white (he only looks white because the concept art is uncoloured). He was scrapped for being seen as an unneeded character in a film with an already large cast.
Simba's mother Sarabi had three sisters: Naanda, Diku, and Dwala. They were all scrapped. Some semi-canon comics and magazines have shown that Sarabi has sisters, but they are never named.
Nala's father was once a character but was scrapped. An earlier idea involved having Mufasa being her father like in real lion prides, however this made her relationship with Simba BrotherSister Incest.
There was a scrapped rock python who would have acted as Scar's Dragon and would have been voiced by Tim Curry. This would be reflected in The Lion Guard where Scar's spirit would have a snake as his Dragon, albeit a cobra rather than a python.
Another scrapped hyena was Baasho, who was Banagi's lackey. Banagi refers to his clan as a "brotherhood", implying that they were entirely male.
In one script Simba was taken in not by Timon and Pumbaa, but by a group of (realistic looking) meerkat called the Komboli Rangers. Timon and his mate Tesma were a part of this group. Simba would have parted with them on his own. In a later script, Tesma was retooled as Simba and Nala's (mostly Nala's) childhood friend while Timon was Simba's childhood friend. Pumbaa (then called "Harold") was also a childhood friend of Simba's.
One of Simba's childhood friends was a female bat-eared fox named Bhati.
Kobi and her son Prita were two unused vulture characters.
Rina and Rada were two minor character ratels.
Nala's name was originally "Nadra". Pumbaa's was "Harold".
Originally, the movie was actually going to end with Simba being the one thrown off the cliff during the final battle against Scar, who then starts laughing maniacally as the fire gradually burns him to death. Fortunately, it then turns out that Simba actually survived the fall.
Very early concept art shows a white cub who was probably Simba. This is commonly thought to mean that The Lion King was a ripoff or unofficial remake of Kimba the White Lion, however at this point in development none of the Kimba similarities existed. It was still in the King of the Jungle stage.
The Lion in the Moon was the God of the lions that was ultimately scrapped between King of the Jungle and The Lion King. He created lions (and possibly all of the animals). Sarabi had a Cut Song where she sang a lullaby to Simba about Him after Simba had his encounter with the hyenas. The comics make reference to a different god, the Great Spirit.
In one incarnation of the King of the Jungle script, Simba had a zebra friend named Lemuta. Lemuta and Simba were playing with an aardvark friend of theirs when Lemuta spots the Ndona pride hunting his herd. Simba's mother Sarabi tries to kill Lemuta's mother, but she manages to escape. Lemuta freaks out at the realization that he's Simba's food and runs away. They don't meet again until they're adults. When Simba tries to talk to his old friend, Lemuta tries to chase him off. Simba is confused about Lemuta's behavior but his father Mufasa tells him that Lemuta is building his own harem now and that he can't be Simba's friend anymore. The Lion in the Moon made them natural enemies so that lions could eat and zebras wouldn't overpopulate.
Concept art shows Simba with rosettes like an actual lion cub, unlike his simplified finalized design. A cub with rosettes wouldn't canonically appear until twenty years later in The Lion Guard (though Simba has them as a newborn).
A good portion of the movie between Simba meeting Timon and Pumbaa and him leaving for the Pridelands was scrapped for being seen as useless filler. Simba was meant to go on adventures, meet monkey characters, and do other stuff but the writers deemed that it got in the way of the Coming-of-Age Story. The Lion King video game features levels inspired by these unused concepts. A gorilla that appears in one of the levels was a deleted character.
Storyboards for Simba returning to the Pridelands had him running through geysers. A level in the video game features elements of it.
In one concept for the beginning of 'Be Prepared', we could have seen Scar initially meeting the leader of the Hyenas alone, which would have shown him charming her. It was cut for reasons of 'ew' and of course, there were more awesome ways to show he was evil than molesting Shenzei.
On the subject of "Be Prepared," Scar has a speaking aside at the start of the song on the soundtrack, in which he denigrates the hyenas. He clearly views them as dispensable tools, rather than deadly partners. Scars aside is not found in the film version of the song, since originally, this song took place before Scar had used the hyenas to try and kill Simba and Nala. Because of the plot adjustment, the song was moved and revised accordingly. The speaking aside was restored for the Broadway adaptation.
Scar was originally going to raise Simba following Mufasa's death. He wouldve been trying to kill Simba, but when spotted by others, he wouldve made it look like he saved Simba and taken him in.
Kiara was originally named Shani. Other potential names were Chaka and Aisha.
Kiara originally had a twin brother named Chaka who was scrapped. Chaka was intended to be the cub shown at the end of the first film, however it was decided that he complicated the story and was dropped. Kiara having a brother was later reused with Kion from The Lion Guard.
Kovu's original name was Nunka. This was a misspelling/variant of "Nuka", which was instead given to his brother.
Vitani's original name was Shetani.
Zira's original name was "Bianca", but it was changed for not being Swahili.
Kovu was originally Scar's biological cub with Zira instead of his adopted successor and the film was even more Romeo and Juliet based. This was changed when they realized that this made Kovu and Kiara Kissing Cousins.note This seems to have been a rather late change in the script, as several languages (Dutch, for example) still confirm Kovu to be Scars biological son.
Mufasa's stint as Rafiki's Spirit Advisor was originally planned to be much more obvious, with the former Lion King's ghost actively speaking to the shaman. Wisely realizing this might come across as unintentionally hilarious, or at least a breaking of the Willing Suspension of Disbelief, the directors decided to instead have all interactions between Rafiki and Mufasa symbolized by the blowing of the wind. This fact is later emphasized when the wind blows around Simba, just before he listens to Kiara and accepts the Outsiders back, and explains why he looks so happy and on the verge of tears at the end, even before he hears Mufasa say "Well done, my son."
We were actually going to see Zira commit suicide by deliberately refusing help from Kiara after accidentally being knocked over a ledge and jumping into the river below so she can drown! Some of the animations of the original death scene was still used; if you watch as Zira falls, you can see the manic grin on her face right as she falls.
Kovu originally had a slicker black mane and brighter green eyes. This was changed when it was decided not to make him Scar's biological son.
One of the deleted scenes that was removed for pacing reasons was of Kovu and Zira. As a cub, Kovu catches a bug and lets it fly away. Zira then catches it and kills it. She scolds Kovu for being too merciful.
There were plans for Zazu (of all characters) to get a love interest in the film, but she was cut from the final product, presumably due to time constraints. Apparently, her name would have been Binti and she would have been voiced by Jane Leeves.
"Diggah Tunnah" had an extra verse that was deleted about a character named "Fearless Buzz". He was a legendary meerkat who thought meerkats shouldn't have to hide underground. Buzz even fought off a hyena on his own, however he forgot hyenas lived in groups and ended up eaten. It was taken out because yet another character added would have made the story become too complicated.
There was a scene where Timon and Pumbaa visit what Timon describes as an "oasis" (when it's really a dump) while looking for their dream home. It turns out they're right next to Mufasa and Simba during the scene where Mufasa describes the previous kings. The scene was removed because it slowed the movie down.