Simba

Simba is the overall tetartagonist of The Simpsons franchise. Initially, he was a sarcastic, loud-mouthed lion that served as X-27's henchman during the latter's attempt to rob Earth of their babies in order to the Martians eat them without any interference from the humans. Simba's primary obsessions are riches and fame, which-coupled with his disdain for the Earthling-motivated his villainous deeds.

Simba's role expanded significantly over the course of the series, the most notable example being the second film, in which Simba reformed and joined Homer, Bunga and Marge as an anti-hero. At the end of the sequel, he becomes the Simpsons' pet lion and Bunga's roomate and close friend.

In the film series, Simba serves as the secondary antagonist In The Simpsons Movie, the central antagonist turned tritagonist in Pollution, a major character in Dawn of the Neptunians, one of the two tetartagonists in The Simpsons: Back to the Multiverse (alongside Bunga), one of the two tritagonists in Fallen Kingdom (alongside Bart Simpson), and the tetartagonist in Dominion. He also serves as a supporting character in Star Wars: The Last Jedi and Star Wars: The Rise of Skywalker.

Personality
Simba is amongst the most complex characters to originate from a 20th Century Fox animated feature film. When first introduced as the loyal follower of X-27, he appears to be as evil and cruel as his superior-being uncaring, murderous, deceitful and cunning. However, Simba is the more aggressive of the two, as well as the more vocal and easily frustrated. He has a difficult time keeping his opinions to himself and has a habit of shouting and ranting on about his annoyances when things don't go as planned.

Like X-27, Simba craves power; the thought of having control over an entire planet (more specifically, the Earth) is what seemingly drives his motivations throughout the original film. Simba cared nothing for those he would have to eliminate to obtain power, and openly expressed his desire to have both Chief Wiggum and Lou killed once he and X-27 kidnaps all babies on Earth; sadistically cackling at the very idea.

Despite being the second-in-command of X-27's nefarious schemes, it was Simba's dilligence that allowed the duo to succeed as far as they did, as it was he who proposed that X-27 run a party to distract the humans while the martians steal the babies and he who eventually captured Marge to attract Homer-using his own unique abilities and wit to do so with relative ease.

He also seems to hate beef (which isn't what you would normally expect for a lion), which Chief Wiggum-apparently being completely unaware of Simba's distaste for them-often fed him directly to the mouth, which also acted as the main reason why he aided X-27 in his treacherous ambitions against the Earth in the first film. After X-27 and the martians kidnapped all the babies on the Earth and attempted to cook them, when attacked by the army created by Homer and Bunga, one of Simba's first actions was exacting revenge against Chief Wiggum by constantly force-feeding him the same beefs he was fed, with Wiggum being unable to fight back due to being tied up by the martians. It's implied in The Simpsons: Dawn of the Neptunians that his hatred for beefs stemmed from a particularly experience at a jungle where he, ironically, did ate meat from animals.

Despite his highly antagonistic role in the original film, The Simpsons Pollution shows a different side to Simba-one capable of growth and reformation. The film implies that Simna's harsh attitude were partially the result of a lack of respect and appreciation over the course of his lifetime. After Homer (seemingly) killed X-27, Simba furiously swears revenge on him, going as far as to steal a spaceship to go to Earth by himself. As an opportunist, Simba cunningly used Lisa's caring nature to get closer to Homer and gain his confidence, so when Homer had completely forgiven Simba, the latter would kill him. However, as the movie progresses, Simba discovers Homer's tragic back story and when the latter risked his life to save Simba's, it was that selfless acted that first sparked a change in the lion's character. He was shocked (and touched) by the prospect of anyone treating him with care and compassion, as even as X-27's partner, Simba faced abuse and neglect. Throughout the course of the film, the Simpson family, most noticeably Bart and Lisa, became increasingly accepting towards Simba, with Marge and Homer even going as far as to consider adopting Simba as the family's second pet despite his attacks against them previously. This would result in Simba feeling guilt and reciprocated care for the family and their friends, prompting him to risk his life to protect Marge from Russ Cargill's henchmen while she was giving birth to Maggie, despite coming dangerously close to death in the process.

Following the second film, Simba has come to understand what must be done to truly earn respect and love: giving it to others. From that moment on, he would remain a loyal friend to the Simpsons. He is still very greedy though, but it's shown that he can be quite selfless as deep down, he appreciates his friendship with Bunga, Homer, Marge, Bart, Lisa and Maggie and shows that he will help them when the situation truly calls for his assistance. He generally tries to avoid danger, however, and often urges the others to do the same. In the episode "The Son Also Rides", Simba and Bunga were told by Homer to keep away from a potentially dangerous quest, which Simba accepts. However, they both spend the entire time worrying for Homer and Bart, to the point where Simba willingly sets out with Bunga to rescue them.

Nevertheless, Simba's villainous nature from the first film doesn't fade completely. He is still every bit aggressive, loud-mouthed, rude and narcissistic, but in a more comedic light than anything; he is no longer willing to result to extreme measures such as murder to achieve his goals. Simba would instead become a mischievous schemer, retaining his flaw of constantly plotting by concocting various get-rich-quick schemes to cheat the citizens of Springfield for their valuables. This ties with his unhealthy obsession with wealth. In The Simpsons: Back to the Multiverse, he was even willing to steal one of the treasures given to Lisa and Milhouse as a wedding gift, as it had the power to lead to a supposed "ultimate treasure". Now with a sense of moral, however, Simba ultimately sacrifices his greed for the greater good (such as the safety of others) in most, if not all occasions.

Bunga
Bunga is Simba's best friend. Although they didn't interact much (if at all) in the earliest episodes, they do so more often in the later seasons, to the point where a lot of episodes subplotes around them, most noticeably the Road to... episodes. Simba and Bunga have a love/hate relationship, in which they constantly bicker and insult each other, yet show affection for each other several times through the series.