Lion is the main antagonist of the 1990 animated film, Little Cornelius. He is a malevolent and manipulative cat who is is willing to kill Little Cornelius and he didn't care about any of the rats and their safety.
Lion is shown to be dim-witted, no-nonsense, cowardly and bumbling cat who's interested in studying mice and caring for their well-being. However, he quickly reveals his true colors of being a manipulative, intelligent, uncaring, and greedy cat who does not care for the well-being animals and only wishes to kill all the mice in the world. He also keeps a pet mouse named Duchess by her side to show he cares for animals, but later kills her as he is disgusted by it. Lion is very social and shows compassion to others by offering his help, but this is a façade to hide his true nature. When he seeing Cornelius for the first time, he tries to kill him with several plans (for example, drowing Cornelius inside the dryer or frying him with a pan) to kick him out of The Littles' house, but fails.
Lion is shown to be a master manipulator as he convinces Kat King to retrieve Cornelius alive in order for him to help him, but truly doesn't care whether the mouse is brought in dead or alive as long as she can make money off of him. Lion became fed up and betrays Kat King to continue his pursuit of the mouse by using his feelings of being laughed at and plans to use Cornelius and kill him to make even more money. When Kat King changes his mind on killing Cornelius, after having second thoughts, Lion takes matters into his own hands by knocking out Kat King and ordering the goons to tranquilize Everest. Lion is willing to harm and commit murder, not only on humans, but also on animals as revealed earlier that he planned to kill Cornelius after betraying Kat King, and later shown when he pushed Cornelius off a tree to his death and tried to ram Willy over with a snowmobile.
Lion hated Little Cornelius for the rest of the life and wanted to kill him to kick him out of The Littles' house. He first appeared when he tried to eat Cornelius, but Mr. and Mrs. Little demand him to spit him out, then scold him to never harm Cornelius, because he’s now a family member.
Lion and the gang then finally encounter Little Cornelius and chase him through the city park and the sewers. Cornelius manages to escape and arrives at the Little House (just seconds after the family has left to search for him) only to be greeted by a deceptive Lion who lies that they were happy he was gone, pointing to Cornelius' empty face on the family photo (which they actually used for his lost posters) and Cornelius leaves, heartbroken. As soon as he's gone, Lion immediately regrets his actions.
A miserable Cornelius returns to the park to make it his new home before an impatient Lion decides to kill both Cornelius and Duchess. The two attempt to flee however Smokey corners Stuart on a tree branch and prepares to lower him down to his subjects, however thankfully Duchess and Willy the Sea-Lion intervenes and snaps the branch causing all of Kat King and his minions to fall. An enraged Lion prepares to move in for the kill against Willy before Cornelius whacks him in the face with a tree branch, knocking him off guard and causing him to fall in the murky pond below.