Gumba is a baboon with long limbs and a narrow body. He has brown fur covering most of his body and a paler brown underbelly. His face, hands, and feet are pink, and he has a large tuft of black fur atop his head. His nose is a darker shade of pink than the rest of his face, and the space between his eyes and his eyebrows is light pinkish gray. Gumba's eyes are dark olive yellow.
Gumba is shown to be thoughtful, spirited, and playful, but quick to pass the blame to others when there is trouble. He admires the Lion Guard and enjoys pretending to be a member of the Guard. He is close to his mother, and won't stray from her side during a crisis.
Gumba and his family are on a large tree, trying to take shelter from the rain. The Lion Guard are already on the scene, trying to persuade the baboons to come down, as the tree is slowly breaking. Kion calls for Bunga to get them out of the tree before the tree collapses, and Bunga uses his flatulence to scare them down. Ono manages to catch Gumba as he falls, and safely delivers him to his mother, just before Beshte's strength gives in and the tree falls down the side of the cliff.
Gumba is first shown walking through tall grass near a pair of grazing zebras. Kion calls him out fiercely, believing that he is ahyenas. Gumba walks out of the grass with his friend Kambuni and assures the Lion Guard that they aren't actually hyenas. Kambuni explains that they were just playing Lion Guard, and Gumba quickly points to Mtoto and tells the Guard that the game was all Mtoto's idea. He and Kambuni then run over to Mtoto and their other two friends, Kwato, and Shauku.
He is next seen while Kambuni tells the Lion Guard about their game. When she mentiones that they all take turns being different members, Gumba adds that Mtoto is the exception to this, as he always chooses to be Beshte. Bunga then asks who gets to be him, and Gumba shrugs and casually replies that it is whoever is last to choose, to Bunga's disappointment. The Guard explains why they shouldn't be pretending to be hyenas, and Gumba promises that they won't do it again. When Mtoto suggests that the real Lion Guard could play Lion Guard with them, Gumba excitedly agrees while moving his hands up and down. But the Lion Guard is busy, and Gumba walks away disappointedly with Kambuni, Kwato, and Shauku.
Later on, when Mtoto announces that he had been training with the Lion Guard, Gumba gives an awed sigh. They all start a new game of Lion Guard. When Mtoto chooses who he wants to be, Gumba, Kambuni, Kwato, and Shauku all finish his sentence for him while rolling their eyes. They begin playing, and Gumba calls out Bunga's catchphrase. He tries to swing on a vine, but it breaks. He sits down and frowns at the broken vine in his hand. Kambuni points out that the game isn't as fun as usual, and Gumba states that it was because they could not be hyenas. Mtoto suggests that three hyraxes could be hyenas, and they all agree and chase after the hyraxes, giving battle cries. Gumba making an "ooh"-ing sound as he follows the hyraxes down a slope.
The hyraxes eventually flee to safety, and Janja, Cheezi, and Chungu arrive, suggesting that they chase the young animals. Gumba and the others cry out "Hyenas!" and flee. He shouts as Cheezi pursues him, but the hyena trips and falls before he catches Gumba. Gumba runs away, in a different direction than Kambuni, Kwato, Shauku, or Mtoto. Gumba and the others then run to Beshte for help, calling his name. They halt in front of him, out of breath and panting. When Thurston dismisses their story, Gumba leaps onto his chest and, waving his hand for emphasis, insists that it is true, and that Mtoto is alone and in danger. He then springs off and watches Beshte leave to help Mtoto.
The Lion Guard locates Gumba and his friends and asks where Beshte is. Kambuni informs them that he went to save Mtoto, and Gumba continues that Beshte went to save Mtoto from the hyenas. Bunga asks
where, and Gumba points and tells them which way. He notifies the Guard that Janja and the hyenas chased them.
Near the end of the episode, he appears listening to Mtoto's story. He listens with his mouth open, impressed. Kion gives Mtoto the Mark of the Guard, and Gumba rushes forward with his friends, asking to be next.
Gumba and his troop are attacked by hyenas as they follow Ma Tembo's Herd to a new water source for the dry season. As the young baboon tries to run he is almost grabbed by Cheezi but is rescued by Fuli. Once saved, he climbs down and continues to follow his troop and the elephants to a dead end (which was the Lion Guard's plan) and Kion uses the Roar to drive Janja's Clan away. He and his troop continue to follow Ma Tembo as she searches for water.