Sometime during Scar's adolescence, the Strange Lion had approached Scar, putting visions of grandiose and desire for more power into his head, with the claim that the most powerful should be king. After leading Scar to the Outlands Volcano, he hid his friend, a cobra from him, and watched calmly as he attacked Scar, leaving him a permanent scar around his left eye.
He then told Scar that as long as he did what he said, he would cleanse the poison within Scar's eye. However, in a fit of pure rage and humiliation, Scar used the Roar of the Elders to destroy both him and cobra, blasting them backwards toward the volcano.
He first appears, in flashbacks, where Scar tells Ushari, in song form, how he had gotten his own scar all those years ago, as informing the cobra was essential for his new plan to succeed.
The Strange Lion was seen early, on July 30th, 2019 via a video on Disney Junior's Youtube channel.
Ford Riley said that he could be related to Zira, but they will not reveal his backstory in the series.
When the lion was revealed in a sneak peek, a popular fan-theory was that he is the father of Zira, due to his similarities in appearance. Another theory was that he is Zira's mate, as in The Lion King II: Simba's Pride it is stated that Scar is not the father of any of Zira's cubs, specifically Kovu. However, this theory proved to be invalid after the episode premiered a couple of days later when it shows Scar killing the lion with the Roar of the Elders making it impossible for the lion to be the sire or mate of Zira.
He had a scar across his eye, the Mark of Evil, that lead some fans to think that he could be related somehow with the Evil Lions of the Past.
It is also theorized that the Strange Lion got his scar via, a cobra bite, similarly to how Scar and Kion got their bites, as he seems to have knowledge about the cobra's venom and the cure.
Despite the lion's death at the claws of Scar, his plans to dethrone Mufasa would come to pass, as the venom in Scar would fuel his dark actions shown in the original film. Which mostly consisted of his desire to be King, leading up to Mufasa's death, and Scar becoming King himself, but not to the lion's satisfaction as Scar would rule the Pride Lands with an iron fist himself. And not being a pawn in the lion's play, as well as Scar's nephew, Simba would return to Pride Rock and defeat Scar.