Tyrannosaurus Rex

Tactics
The T-Rex has many ways to kill Lara, so it's really a death wish to stay near it.

Tomb Raider
There's a cave in the valley where you can take shelter and shoot him at the same time. It's the best way to kill it. You 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 until it's death.

Tomb Raider 2
There are two at the same time! To safely kill them, stay in the little hole where the third secret was.

Tomb Raider 3
Right after you grab the key that was in his nest, he 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 him from a distance. Staying in the deep water is also a safe way to kill him.

Appearances

 * The Lost Valley(1)
 * The Great Wall(2)
 * Nightmare in Vegas (2)
 * Crash Site (1)
 * Peru - The Lost Valley (1)

Trivia

 * The T-Rex in TRA, as the commentary states, is probably much larger than a real Tyrannosaurus Rex would be.
 * There's a T-Rex trophy inside the treasure room in Tomb Raider III.