Simba is an African lion who lives in the Great Circle of Life (song "Circle of Life"). He is the son of King Mufasa and Queen Sarabi and is next in line for the throne. His uncle, Scar didn't attend his presentation because he was jealous of his nephew. Scar was next in line for the throne before Simba was born.
As a cub, Simba was excited to be the next king of Pride Rock (song "I Just Can't Wait to be King"). He and his best friend, Nala both snuck into an elephant graveyard Simba's uncle, Scar told him about and his father and father's assistant, Zazu, forbid him to visit. The two cubs are almost killed, but Mufasa rescues them.
Mufasa then tells Zazu to take Nala home and has teach his son a lesson, scolding about his deliberate disobedience and putting Nala in danger. Simba tells his father: "I just wanted to be brave like you." His father then tells him that he's only brave when he has to be, and he was scared because he thought he might lose him. The two then play together and Simba makes a remark that they'll always be friends and always be together. Mufasa tells him to look at the stars in the sky, and that the Great Kings of the Past and are always watching out for them. Afterward, Scar sent a trap so Mufasa would die in a stampede and sent Simba away, making him believe it was all his fault and the hyenas threatened to kill him if he returned.
Simba grows up and tries to leave his past behind and he enjoyed his new life with Timon and Pumbaa. He is reunited with Nala after stopping her from trying to catch and eat Timon and Pumbaa. They fall in love, but argue about his past. Rafiki finds Simba and helps him see Mufasa's spirit, and he is reminded that he is his son and the rightful king and must take his place in the Circle of Life. Afterward, Simba decides to go back to Pride Rock. He sees the devastation and his mother, Sarabi being knocked down by Scar. She is shocked and happy that Simba is alive, and Nala and the other lionesses stand up to Scar, telling him that Simba is the rightful king.
Simba and Scar fight, and Scar is forced to admit that he killed Mufasa. Scar was defeated and Simba took his place as king with Nala as his queen.
He banished Scar's followers to The Outlands, and came across Kovu, a cub Scar hand-picked to become king. His mother, Zira, is Scar's most loyal follower and she was training Kovu to kill Simba. A few years later, Kovu rescued Kiara from a fire, but Simba wasn't convinced that he left the Outsiders and became a rogue. Simba believes Kovu is following in Scar's footsteps. He forbids Kiara from being with Kovu even after Kiara told him he loves her for her. Simba said he's following his father's law and Kiara tells her him: "You'll never be Mufasa!" and runs away from home.
During the fight with the Outsiders, Kiara and Kovu stop the fight and Kiara reminds her father: "We are one." Simba accepts Kiara's words, but Zira attacks and Kiara stops her. After they fall off a cliff and Zira is killed, Simba helps Kiara with his outstretched paw and apologizes to Kovu, saying he belongs with the Pride. He then tells the Outsiders: "Let's go home - ALL of us." Simba has Rafiki bless Kiara and Kovu's union and they take their place with Simba and Nala at Pride Rock. Mufasa's spirit says: "Well done, Son. We are one."
The adult Simba is voiced by Matthew Broderick and child one voiced by Jonathan Taylor Thomas.