|“||I don't eat junk food.||„|
|~ Diego to Sid, who is unaware that 'junk food' means him|
|“||Excuse me, I am not soft. I happen to be a remorseless assassin.||„|
|~ Diego after being called soft by Shira|
He is a (former) secondary antagonist turned deuteragonist of Ice Age, the tetartagonist of Ice Age: The Meltdown and Ice Age: Continental Drift, a major character in Ice Age: Dawn of the Dinosaurs, Ice Age: Collision Course, and the Christmas Special, and the tritagonist of the Easter Special.
Before meeting the herd, Diego was a wild, vengeful, aggressive, and ruthless saber-toothed cat. He was blindly loyal to his pack and their leader Soto who both shared a mutual respect for one another and was tasked with retrieving the baby from a human tribe as revenge for them killing nearly half of their pack. However, when he failed, Diego would either find the human baby or die.
After meeting Manny and Sid who were protecting the child he was supposed to deliver to Soto, Diego tricked them into going to Half Peak where he says the baby's parents are waiting but his pack is and will kill the three of them, showing that he was quite uncaring. At first Diego and Manny's relationship had an incredibly rocky start, the two didn't trust one another nor value either as friends. However, as they continue their journey, Diego discovers Manny's tragic backstory and when the mammoth risks his own life to save Diego's, the two became extremely close friends. His relationship with Sid, on the other hand, was an instant dislike and constant annoyance. On more than one occasion, he came close to killing him with his teeth. However, the two have a very strong bond and are close friends possibly more than Manny even if the two might not trust each other.
Throughout the entire film, Diego was seen as having conflicted loyalty between his Pack and his herd. Eventually, his loyalty between Manny and Sid was strong enough to defy Soto and defend his friends from the pack even on his apparent deathbed. He proved to be loyal enough to give Manny and Sid the true directions to the human tribe so they can return the baby. However, it turns out that Diego survived his wounds and has decided to join the herd with his friends.
In The Meltdown, Diego has adjusted to Herd-life. He has a sarcastic and even at times a vicious sense of humor most commonly at the expense of Sid such was shown when the sloth was about to perform a near-suicidal stunt and like the rest of the crowd he chanted "jump." This was also shown during the fourth film when his prisoner, Shira refused to take water for him to reply in a dry tone "fine, die of thirst that'll show me."
It is revealed that Diego suffered from severe hydrophobia, as said by Sid, he was "letting the water make it his prey" and could neither swim nor even touch it without going in a fit of terror. He also proved to be very prideful specifically about his reputation, when he and Sid had been pinned down by Eddie and Crash, two possums Diego replied that if anyone asks there were 50 rattlesnakes.
At times, Diego can be quite selfless and altruistic, when he saw that Sid and the possums were trapped in an upstream lake he dived in headstrong to save both of them and ignored the fact that he couldn't swim or that he was completely terrified of water. Another time was when an entire herd of mammoths arrived unexpectedly, he and Sid implored Manny to go with Ellie only for all of them to stick together and become their herd.
Given Dawn of the Dinosaurs, Herd-life has shown to affect Diego, he appears to have lost his edge left exhausted while trying to chase a gazelle and then mocked by the latter, his solution was to leave the Herd behind and become sort of a lone wolf. He still showed immense bravery and loyalty towards his friends, after Sid was abducted by a Mother Dinosaur, he entered the dinosaur world without knowing what was lying within there to save his friend. In the end, Diego decided to stay with the Herd.
By Continental Drift, Diego is once again a true member of the Herd. It is unknown whether he would have murdered Sid's Uncle Fungus as a sort of revenge for being nearly run over by him because it was interrupted by the sloth. He was also very suspicious and reluctant to tell Sid that his family had abandoned him once again showing that he doesn't enjoy hurting his friend's feelings however he covered this up with an abominable lie. Diego at times can be the more practical of the three, an example would be when Manny was about to jump past a gorge only to be stopped by Diego as he would never make it. When they were trapped on an iceberg ship with no way back, Sid repeated a saying that his mother told him only to bitingly reply that this was before she abandoned him.
During the film, Diego had a romantic relationship with another saber-toothed tiger named Shira, the first mate of a band of pirates. However at first the two barely even liked one another, the only reason they stuck together was that they were shipwrecked. After an attempt to escape Shira became the prisoner of the Herd and discovered that the two have much in common, Diego was able to let Shira see through her Captain Gutt's cruelty, Shira saved the Herd from the wrath of the captain after this Diego developed romantic feelings for her. Near the end of the film, Shira became a member of the Herd and fought against Gutt and the rest of the pirate.
In the first film, he was part of a pack of saber-toothed cats (which was also made up of Zeke, Oscar, and Lenny) 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 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 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.
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.
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.
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.
- Originally, Diego was stated to die in the first movie, but he survived in the final cut because it was too depressing for the kids in the test audiences. Denis Leary warned the producers that this would happen. When it proved true, he got his wish and Diego remained alive.
- 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, Diego's story was about his double agency.
- In Ice Age: The Meltdown, Diego's story was about him overcoming his Aquaphobia.
- In Ice Age: Dawn of the Dinosaurs, Diego's story was about leaving the herd before trying to rescue Sid on his own. (Later, he rejoins the Herd)
- In Ice Age: Continental Drift, Diego's story was about him meeting and falling in love with Shira, a female Smilodon.
- In Ice Age: Collision Course, Diego's story was about him and Shira deciding whether to have any children or not.
- It was in Ice Age: Continental Drift that Diego and Shira had their first kiss.