"I intend to eventually destroy all of mankind right down to the very last speck of dust."
Killed lots of people. Tortured Vash. Fulfilled Knives' final order. WOKE UP.
Killed lots of people (oho a pattern). Got sucked into the Labyrinth. Went to Sleep. Woke up. Trolled. Was Unmade during the final fight with the Dark Aeon.
Was roughly 6'3" with blue hair and gold eyes. Called a "lady killer" and described as being "almost sickeningly pretty", but his total lack of expression made for serious creepy times. BUT NOW HE'S UNMADE SO THE CREEPY PRETTY IS GONE.
Sure did kill people WITH HIS MIIIIIND.
THIS SURE IS OLD AND LACKS AND AYA, WHO WAS MEGA IMPORTANT TO HIM. But Legato was Unmade so whateverrrrrrrrr.
Alexander Wolfgang: Legato tried, and ultimately failed, to kill Alexander. However, he got an interesting look at the man's mind in the process. And, by forcing him to kill Sari, he was certainly able to make the man suffer. Although they met and spoke later, Legato had no idea the disguised man he was conversing with was Alexander.
Cain: Not human, and therefore not a target. He appears to despise humanity. Naturally, Legato thinks he's rather interesting.
Crawford Sands: A foul-mouthed man who was building explosives. Legato forced him to light one of those explosives and blow himself up. Since then, he's also forced him to stab himself in the neck and bash his own face in with a hammer. Unfortunately for him, he's become the subject of experimentation for Legato.
Firo Prochainezo: Another man that Legato attempted, but ultimately failed, to kill. Or rather, he did kill him, but Firo simply kept reviving.
Lelouch vi Britannia: A man that sounds almost exactly like Vash the Stampede. Legato naturally zeroed in on this and wouldn't leave Lelouch alone until he saw his face. After he backed off a bit, Lelouch gave him directions to the Western District's Welcome House. Despite knowing that Lelouch is most certainly not Vash, he still sometimes thinks that it's Vash speaking over the network.
Jamie Hemeros: A teenager who Legato murdered by forcing him to walk out into the Northern Plains. He was devoured by a T-Rexaur while Legato enjoyed a nice ice cream sundae.
Jazz: After Legato arrived in Nautilus with no powers, it was Jazz who told him how to go about getting them back. Ironically, Legato later used those same powers to kill Jazz while the Cybertronian was in human form. He was the first non-human that Legato killed, and, upon realizing this, he wasn't entirely sure how to feel. However, he was quickly convinced that the Autobot deserved to die as much as any human.
Ratchet: When Legato arrived in Nautilus bleeding from the back of his head (the remnants of the gunshot wound that killed him), Ratchet was the one who fixed him up. It was Legato's first encounter with Bending. He also gave Legato the Welcoming Guide. After forcing Alexander to kill Sari, Ratchet met and spoke with a grieving Ratchet, but gave no indication that he was the one responsible.
Sari Sumdac: A young girl who Legato forced Alexander to kill. Because of her Cybertronian heritage, he was unable to fully control her body or look inside her mind. Currently, Legato doesn't know that was the reason.
Soundwave: A Decepticon that believes inferior beings need to be put in their place. They've formed an alliance, and get along quite well. Soundwave is the only one who knows that Legato is behind the recent string of murders in Nautilus.
Xemnas: A Nobody, and therefore not a target. Legato finds his speeches, as well as his lack of caring for the well-being of others, to be quite interesting.
Zane: As a test of his powers, Legato forced Zane to tear his own heart out. He didn't even know his name.
A few of the tropes that can apply: Big Eater, Complete Monster, Creepy Awesome, Creepy Monotone, Dissonant Serenity, The Dragon, Even Evil Has Standards, High Octane Nightmare Fuel, In Love With Your Carnage, Kill All Humans, Nietzsche Wannabe, Psycho Supporter, Slasher Smile, Spikes Of Villainy, The Stoic