Doppelgänger
In the original Tomb Raider game and Tomb Raider: Anniversary, Lara encounters the doppelgänger, a creature of no skin and no hair, who imitates Lara's movement. At the end of the Great Pyramid, Lara first encounters the doppelgänger, but kills it by tricking it into falling into a lava pit. In Tomb Raider: Anniversary, it is also an unlockable costume for Lara. It is unlocked by collecting one relic in lost island levels.
In Tomb Raider: Underworld, Lara encounters another doppelgänger. However, this one no longer copies Lara and makes its own movement, and is mainly ordered by Natla. The new doppelgänger looks just like Lara, with skin and hair, but she has yellowish eyes, red braided hair, paler skin, a different outfit, and has a superhuman ability to move around extremely fast. The new doppelgänger is first featured blowing up Croft Manor in the teaser trailer. She did not speak at all throughout the whole story.
When Lara's manor is on fire, Zip says that the doppelgänger tried to shoot him, which he had first mistaken for Lara. Later on, when Lara is checking the tech room to find out where Alister is, and who opened the vault to blow up her manor, she meets the doppelgänger for the first time, who also kills Alister as he is passing by. Lara opens the tech room door and starts fighting with the doppelgänger, although it is very fast and can dodge Lara's bullets. When Lara is on the floor, she runs out through the high level of the burning building, jumping distances beyond Lara's ability to jump. The doppelgänger is found again on Amanda's ship in the Andaman sea. When Lara faces with Amanda, the doppelgänger is seen to be looking at Natla, and throws Amanda far into the ground. Lara again tries to kill the doppelgänger with Thor's hammer, but being faster than she is, the doppelgänger escapes the bolts from the hammer. Later on, in Helheim, the doppelgänger is seen once more. She again tries to kill Lara by pinning her to the ground, however, the doppelgänger is suddenly lifted into the air and thrown into the eitr by Amanda, saving Lara.
Following the events in Helheim, the doppelgänger is seen again in Beneath the Ashes and Lara's Shadow. In Beneath the Ashes, it appears at the very end of the level. Lara uses the Eitr Stone to command a newly risen thrall to attack the doppelgänger, who easily defeats the thrall and moves to attack Lara, only to be stopped at the last second when Lara utters the "magic word" on the Eitr Stone to assume command of the doppelgänger. Issuing it only one command, "make Natla suffer", the doppelgänger disappears.
In Lara's Shadow, it is shown how the doppelgänger survived Amanda's attack: she was knocked unconscious after landing on the floor below. Later on in the level, it is also revealed that Natla is still alive, but severely injured. The doppelgänger finds her by the stone dais in Helheim, and obediently returns her to the pod in which the doppelgänger was created. The doppelgänger returns to Lara's mansion in order to kill her, but Lara uses the Eitr Stone to disrupt Natla's control, giving the doppelgänger free will.
In order to "make sure Natla suffers", the doppelgänger returns to Natla and destroys her pod, causing Natla to fall into the eitr. The Atlantean Queen tries to command the doppelgänger once more and save her, but it is no longer a slave.