Diego is a sabre toothed tiger and the tritagonist of the Ice Age franchise. He is one of Manny's best friends and one of Peaches' adoptive uncles. He becomes Shira's lover or husband in Ice Age Continental Drift
In Ice Age
In the first film, he was part of of a pack of saber-toothed cats led by Soto, their vicious leader who hated a tribe of human hunters for killing half of their pack. Diego was tasked with getting a human baby from a tribe of humans so that Soto would have his revenge on the humans by killing the baby to send the humans a message they would never forget. Diego, however, failed to retrieve the baby due to the mother's intervention and self-sacrifice. Soto then ordered Diego to get the baby or face being killed by his own pack if he failed again. Diego then encountered Manny and Sid, who had already found the baby before he did. Diego then volunteered to lead both the baby and Manny to Glacier Pass, while secretly leading them to his pack at Half Peak to kill them. But after Manny risks his own life to save him from falling into a river of lava, Diego has a change of heart and then tells Manny and Sid of his pack's plot, blowing his own pack's cover. In a fit of rage, Manny pins Diego to a rock wall with one tusk, and pressed the other tusk's point against Diego's throat, intending to kill the saber-tooth. Diego pleads for Manny to trust him as he forms a plan. However, the plan goes wrong as Soto appears around the corner, inviting Diego to help kill Manny. At first, he appears to side with Soto, growling at Manny. But then he stands in front of Soto, and coldly told him to "Leave the mammoth alone." Oscar and Lenny, (Who had been unconscious at the time), attack Manny. Diego then fights Soto (the scene could be compared to when Simba fights (Disney) Scar in The Lion King). Diego ends up severely wounded after intercepting Soto's attack. Manny then knocks Soto into a wall and icicles fall and impale him to death. The seemingly dying Diego tells the herd to leave him before they lose the humans, sacrificing himself to ensure the baby's return. However, in the end, Diego recovers from his injuries and catches up with Manny and Sid in time to say his last heartfelt goodbye to the baby and happily decides to head south with them.
In Ice Age: The Meltdown
In the second film, Diego reveals his hidden fear of water. Sid, the only one who knows about Diego's fear, teaches him how to overcome his fear of water. When Sid becomes unconscious after hitting his head on a block of ice during an attempt to save Crash And Eddie. Diego, through Sid's advice, overcomes his fear of water and saves Sid and Crash and Eddie.
In Ice Age: Dawn of the Dinosaurs
In the third film, after failing to catch a gazelle, Diego fears that his time with the herd has made him soft and decides to leave the herd. He then later joins the herd in finding Sid who was taken by Mommy T-Rex. Later in the film, Diego protects a pregnant Ellie from a pack of hungry Guanlong. In the end, he decides not to leave the herd.
In Ice Age: Continental Drift
In the fourth film, he meets a saber-toothed tigress named Shira when Manny, Sid, Diego and Sid's grandmother rescued her. Diego then starts to have feelings for Shira and convinces her to join him and his friends. In the end, Diego and Shira fall in love with each other and become a couple.
In the future, Diego marries Shira and have a litter of cubs with her.
- Diego and Shira are equivalents of a male African lion and a female White Tiger.
- Diego plays the bravery in the Herd. (While Manny is the brains and Sid is the comedy).
- In each ice age movie, Diego has his own side story:
- In Ice age 1, Diego's story was about his double agency.
- In Ice age 2, Diego's story was about him overcoming his Aquaphobia.
- In Ice age 3, Diego's story was about leaving the herd before trying to rescue Sid on his own. (Later, he rejoins the Herd)
- In Ice age 4, Diego's story was about him meeting and falling in love with Shira, a female Smilodon.
- Diego is similar to many heroes who have formerly worked for the villains before siding with the heroes to bring down the villains with a change of heart about their ethics, including John Smith, Pheobus, Kovu, James P. Sullivan, Neera, Bruton, and his love interest, Shira.