Tyrannosaurus Rex

 (abbreviated to T.rex) is a dinosaur appearing in a multitude of Tomb Raider games.

Tactics
The T.rex has many ways to hurt or kill Lara, so it's really a death-wish to stay near it. The T.rexes in the first three games can damage Lara by touch and possess a bite attack that will instantly kill Lara if it makes contact, resulting in a death animation. The T.rex in Tomb Raider: Anniversary has multiple bite attacks and will use a tail whip attack if Lara is right behind it. It can knock Lara to the ground by touch, diminishing some of Lara's health. It will charge when it gets enraged from repeated shooting.

Tomb Raider / Tomb Raider: Anniversary
First appearance of the Tyrannosaurus Rex in the series. It is encountered in the lower valley section of the Lost Valley level. Its existence is hinted by the presence of other dinosaurs in the area, a broken wooden bridge seen above, but most importantly by a series of gigantic footprints on the ground. Once having approached the wooden bridge enough (about when stepping the second-to-last footprint), the T.rex will make its dramatic entrance, charging at full speed and making the ground shake as it does so.
 * Tomb Raider

The tyrannosaur is extremely powerful, resilient and fast; it can traverse the entire valley –back and forth– in just a manner of seconds. It has a powerful biting attack that can instantly kill Lara, and the stompings it does as it moves deal heavy damage, almost counting as a secondary instant kill attack. All these abilities in conjunction make the T.rex not a recommendable enemy to fight head on, so it's better to use brain over brawn in this encounter.

There are a number of enclosed alcoves and niches along the walls of the valley Lara can use to take cover from the beast, although just partially, and potentially putting her at risk of being cornered. A better strategy is to rush to a ground level cave that is located right below the wooden bridge, on the right wall; this will lead Lara to a vantage point where she can freely shoot at the creature without it being able to retaliate in any way.

If, on the other hand, the player wants to take the fight up and personal with the T.rex, then they can also use the shotgun from close range to make quick work of it. Another way is to equip the pistols as soon as possible, and back flip and shoot it until it dies.

The battle against the T.rex was recreated in Anniversary, the re-imagining of the classic original Tomb Raider game. However, the tactics are different this time around, especially with the introduction of the adrenaline dodge move. Before the fight, there will be a quick-time event, so follow the required button presses; then the real battle begins. You must shoot the T.rex until its rage bar fills up completely. Once it gets enraged, stop shooting but keep your guns drawn and try go in front of one of the three spiked structures that are placed along the perimeter of the battle arena; each of them has a patch in front in a lighter tone of grass to help you tell where it is located while you're focused shooting at the beast. When the T.rex attempts to attack you by charging, dodge to the left or right, and when the two red reticules overlap, immediately shoot. If the T.rex hits the spiked structure, it will take away one-third of its health meter. This means that it takes bumping into the three spiked structures to defeat the dinosaur. While making the T.rex run into the mountain wall or anything other than those spiked structures still does some damage, it won't lose anywhere near as much health. Once the T.rex's health reaches zero, another quick-time event will ensue, so just follow the required button presses to finally take down the beast.
 * Tomb Raider: Anniversary

Tomb Raider II
There are two in the same area! Though the second one only appears when you leave the small hole containing the third secret. To safely kill them, shoot while staying in the little hole where the secret was until they go down. Another strategy is to kill the first T.rex before spawning the second one. These T.rexes have around the same amount of health as the one from the first game.

Tomb Raider III
Right after you grab the key that was in its nest, it appears. Run as fast as you can to the small cave with a lever (it is right at the side of the slope that you used to get down) to kill it from a distance. Staying in the deep water is also a safe way to kill it. Unlike the T.rexes in the previous two games, this one has an immense amount of health in comparison.

Lara Croft: Relic Run
A T.rex appears as a boss of Cambodia's Jungle Temple. Easiest way to kill it, is with maxed-out Crossbow. If you are fast enough with the clicking, you can take out T.rex with two encounters (gets tougher after every kill).

Tomb Raider reloaded
T.rex appears as a boss of stage 50 of Chapter 4 - The Lost Valley. The mechanics are slightly similar to the one in Tomb Raider: Anniversary where, he can be lured into spiked walls for more damage.

Tomb Raider

 * Lost Valley (1)

Tomb Raider II

 * The Great Wall (2)

Tomb Raider III

 * Crash Site (1)

Tomb Raider II: Golden Mask

 * Nightmare in Vegas (2)

Tomb Raider: Anniversary

 * Peru - The Lost Valley (1)

Lara Croft: Relic Run

 * Jungle Temple (2)

Tomb Raider Reloaded

 * The Lost Valley, Stage 50 (1)

Trivia

 * The T.rex in Tomb Raider: Anniversary, as the commentary states, is probably much larger than a real Tyrannosaurus Rex would be.
 * There's a T.rex trophy inside Lara's treasure room in Tomb Raider III.
 * Tomb Raider II, Tomb Raider III, and Lara Croft: Relic Run T.rexes have 3 digits on each hand, whereas the one in Tomb Raider and Tomb Raider: Anniversary have the correct number of digits; that being 2. It can be pretended that the giant dinosaurs we see in Tomb raider 2-3 aren't actually T.Rexes at all, and instead one of the carnosaurs such as Giganotosaurus, Allosaurus, Carcharodontosaurus, or Saurophoganax. However, the TR3 case confirms that the large, 3 fingered dinosaur in Crash Site is indeed a T.rex.
 * The T.rex in Tomb Raider III will sometimes respond to the flare that's dropped on the ground by the player. This is most likely a reference to Jurassic Park.
 * The T.rex in the first Tomb Raider will completely ignore any Raptors that are present whereas the one in Tomb Raider III will decide to fight and kill any Raptors that are near it.
 * In TR1, when the T.rex dies, its corpse is still tangible, meaning the player can't run through the body. In TR2 and TR3 however, the T.rexes' body become intangible when they are killed, so the player can run through them.

Appearances

 * Tomb Raider: Featuring Lara Croft (First appearance)
 * Tomb Raider II: Starring Lara Croft
 * Tomb Raider III: Adventures of Lara Croft
 * Tomb Raider II: Golden Mask
 * Tomb Raider: Anniversary
 * Lara Croft: Relic Run
 * Tomb Raider Reloaded