As a child (cub), Simba is curious, adventurous, cocky, and all too ready to become king. He is known to overstep his authority and attempt to order around the other creatures of Pride Rock. He suffers serious emotional trauma when Scar, his uncle, murders his brother, Simba’s father, Mufasa. He didn’t know this however, and Scar convinces Simba that he was responsible for his father’s death, and tells him to flee from the Pridelands, never to return. Simba naively shows great trust in his uncle as he runs away from all he’s ever known, and he later picks up a happy, carefree lifestyle with Timon and Pumbaa in an idealistic jungle paradise.
As a young adult, he has long since forgotten his old life, and once again acts as over-confident and adventurous as he did as a cub. Later, when Simba learns that Scar is ruling the Pridelands unjustly, he faces his past and returns to take his place as the rightful king. By having the responsibilities of being a king thrust upon him so suddenly, Simba is forced to mature greatly, and in a short space of time.
As an adult, Simba has grown much more mature and responsible. Yet he is ammensely paranoid, distrusting, and over-protective, in regards to his only daughter and heir, Kiara. He always has Timon and Pumbaa, now his royal advisers, to keep an eye on her and even marks a trail when she ventures alone. This doesn’t change when Kiara matures into a young adult because Simba breaks a promise to her for the sake of her safety.