Diego is the tritagonist of the Ice Age franchise.
He is a saber tooth tiger who starts off as an antagonist, but soon becomes Manny and Sid's best friend and one of Peaches' adoptive uncles. He becomes Shira's lover or mate in Ice Age: Continental Drift.
He is voiced by Denis Leary.
Before meeting the herd, Diego was a wild, vengeful and ruthless sabre-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 actually his pack are 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 obviously 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 actually 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 totally trust each other.
Throughout the entire film Diego was seen 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 could 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 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 really show me."
It is revealed that Diego suffered from severe hydrophobia, as said by Sid he was "letting water make it his prey" and could neither swim or 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 fifty rattlesnakes.
Diego at times can be quite selfless, 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 own herd.
Given Dawn of the Dinosaurs, Herd-life has shown to have an effect on 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 actually 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 reluctant to tell Sid that his family had abandoned him once again showing that he doesn't enjoy hurting his friends feelings however he covered this up with a totally 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 sabre-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 actually stuck together was because 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 actually 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 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 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 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 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 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 met up with his friend Manny at a fruit bar, where tiny hyraxes were giving them various fruity drinks. Manny began talking about how weird Ellie acted and asked Diego if Shira ever giggled. Diego glanced to the side, where he saw his wife ferociously chasing an elk. Somewhat intimidated, Diego responds that Shira isn't much of a giggler. Manny and Diego found Sid, with poison ivy burns. Despite the sloth's attempt to convince his friends that everything was fine, Diego accurately guessed that his girlfriend, Francine, dumped him. Manny then took Sid to get him cleaned up.
At Manny and Ellie's anniversary party, Diego grabbed some grapes, along with Shira. The sabers watched some kids play around. The grape juice dripped down on their chins. Diego told Shira he keeps imagining their own kid and that he'd be the best one. Shira disagreed, saying he meant "she". Unfortunately, they are reluctant to have kids because as Shira points out, children run away every time they see them. Two kids, a Young Start and Young Aardvark, came across Diego and Shira and saw the juice dripping down their chins and their glowing eyes. Even though Diego and Shira acted friendly, the kids thought the juice was blood and ran away in fear. This left the sabers confused, as Shira even points out she smiled this time.
Sid then pointed out a "fiery ball" in the sky. Diego went to go tell Manny that they had a problem. Manny said his problem was more important. Diego eventually got Manny's attention and they made a run from the meteor and went into an Ice Cave until they thought in was safe.
Later, they found their old weasel pal, Buck. Buck told them an asteroid was coming and lead the herd. They later were stuck in an electrical storm. Diego saw his fur was puffing up by his paw. Later Diego whole fur fluffed up. Manny and Ellie got stuck by the lightning and Diego saved them. Buck heard a baby crying and ran into the forest. He came out of the forest with a baby pumpkin named Bronwyn. The herd thought it was strange. Before the herd continued off on their journey, Diego caught the scent of some scattered feathers lying around, sniffing them suspiciously until they were blown away. Buck told the herd to rest the night and Diego and Shira rested together.
After escaping the forest, Diego is seen having a friendly conversation with Julian. The two even perform a cool "peace-out" gesture. When Manny shows displeasure towards this, Diego attempts to convince him that Julian is a good kid and he should try bonding with him. During a hockey match, Manny accidentally hits Julian with the puck and causes him to fall through the ice. Displeased at this, Diego sarcastically says it's a mystery why Peaches wants to move away after the marriage.
In the morning they found that Granny was missing and that there were more scattered feathers lying around where the herd slept. Buck ended up revealing that there was a family of Dino-Birds that chased after the herd the entire time. The herd suspected that the Dino Birds must of eaten Granny, and thought she was gone for good. That was until they heard her yells and followed them.
They found Granny was getting massages by a prehistoric rabbit called Teddy. They found themselves in Geotopia, a place of crystals, and where people stayed in their youth. Brooke, a ground sloth, fell in love with Sid, and called her squad of minicorns, called Bubbles and Misty. The minicorns tapped their hooves on the crystal ground, causing a crystal hoverboard to be released, to take them to the Geotopian leader, Shangri Llama. Granny voiced her disgust saying llamas spit and smell bad. Diego took the chance to amuse Shira by pointing out Granny isn't very different. The herd tries to warn Shangri Llama about the asteroid, but end up having to stretch to get his attention.
After Sid accidentally breaks the Geotopian wall, the Shangri Llama throws a fit. Seeing this Buck gets the idea to seal the steam vents around a nearby volcano to throw the asteroid elsewhere. Diego voices doubt at the plan so Buck continuously pokes his nose until he roars, demonstrating "tremendous pressure leads to a tremendous explosion". However the Shangri Llama isn't willing to give up the eternal youth that the crystals provide. With some convincing from Brooke however, the Geotopians go along with Buck's plan. After the asteroid is sent back into space, the herd celebrate their victory.
As Diego and Shira wait for Peaches to get ready, they are approached by the same start and aardvark from the anniversary party who ask about their adventure. The sabers begin to tell the kids how they came to stop the asteroid. With their new bond with the kids, Shira happily told Diego they'll make wonderful parents one day. Once Peaches officially became Julian's wife, Brooke sang My Superstar, for which Diego and Shira danced to along with the young aardvark and start.
- 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 actually 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.