Legato Bluesummers (レガート・ブルーサマーズ)

Legato's telekinetic powers come from the fact that he has Vash's left arm. When Knives shot it off, it was attached to Legato. This is why Legato can control other people's bodies (originally one of Vash's and Knives' powers) and can activate Vash's angel arm the same way Knives did in July.

It is unclear how Vash's arm was transplanted to Legato, since Vash is a humanoid plant and Legato is human. One might think that perhaps Legato is also a humanoid plant, but it is made clear in the series that Legato is human and hates himself because of it. Thus we can only assume that Knives somehow "reconstructed" and modified Legato in some way.

In the manga, Legato uses metal threads, implanted in his brain, to control others as well as create barriers. A prime display of this ability is when he used in his first encounter with Knives as a child. He used this power to survive Knives' attack and impressed the killer to such a point that he allowed him to become his right-hand man.

In the manga, the skull on Legato's left arm opens up to reveal a mechanical spindle with all the micro-wires he uses to control people. It is merely decorative in the anime.