Askari has a golden-brown fur pelt, a white muzzle, and a dark orange nose, a light golden underbelly, as well as a large red mane, (similar to Mufasa’s) with darker red edges and golden stripe markings. He has a long chin and defined cheekbones, with small yellow eyes with red markings around them.
Askari is a brave, noble lion who believes in peace between animals that are capable of such feats. He teaches Kion about the powers of the roar showing that he is knowledgeable. He also believes in defending and helping the Circle of Life even outside of the Pride Lands since he knew that the Tree of Life could use the Roar's help.
Prior to The Lion Guard
That's the secret they created to defeat great evil, Askari's original Lion Guard.
Before Askari was the leader of the first Lion Guard, he was the Prince of Pride Rock and the second-born cub of the monarchy, and the younger brother of the future Lion King. Sometime in his adulthood, the Pride Lands in his time was about to be taken over by a group of evil lions that almost destroyed the kingdom. To stop them, the good lions of the Pride Lands formed a powerful force where the worthiest in the kingdom would be chosen to stop them, giving rise to Askari being the leader of the Pride Lands' first Lion Guard. Sometime during his life, he discovered the Roar of the Elders at the Tree of Life and learned to master its powers.
During one of his many adventures as leader of the first Lion Guard in the Pride Lands, he and his team made a peace pact between the elephants and the lions of the Pride Lands believing that both creatures are wise enough to work together in harmony. He also led a group of animals to Mizimu Grove, though for what reason has yet to be told.
Sometime after this, he passed away, leaving his legacy behind, and starting the tradition of the leader of the Lion Guard, which would be passed down from generation to generation through his brothers' descendants, most notably Scar and Kion with the notable exception of Vitani who is the sister-in-law of Kiara and daughter-in-law of King Simba.
Askari was mentioned several times when the Lion Guard and Makini went deep into the lair in order to find the secret of defeating a great evil. Askari and his Lion Guard left many hints as to what sort of dangers they would encounter along the way, making sure that only the worthiest would ever find the Chamber of the Lion Guard and, along with it, the secret to defeating a great evil.
Askari meets Kion, aware that he is the leader of the new Lion Guard when he hears his distant relative accept that the Roar wasn't the thing that made him a leader and that he doesn't need it. Happy with his resolve, Askari thought that it was time to teach Kion all the powers of the Roar.
When Kion decides to let go of the Roar, Askari appears to the Pride Landers praising Kion for his decision and having mastered the Roar because of it. However, when his distant relative asks why he still needs it if he's not the leader of the Lion Guard anymore. That's when he mentions that there is another place that could use the Roar's help, speaking of the Tree of Life and encouraging Kion to return there. His spirit later appears with Mufasa's and Janna's as Kion becomes Queen Rani's mate, ruling the Tree of Life with her and seeing the Roar of the Elders now finally return to its true home at the Tree of Life and proper place in the Circle of Life.
Askari is the only lion on the show to have sclerae that are darker than his irises.
Nothing is revealed about Askari being somehow related to either Mufasa, Simba or Nala. But still fans assume that he must be related to them at some point, because he is important enough to the family to appear to all of them in the finale.