Deathstroke

"I was hoping someone else had offed you, and that you were visiting your dear mom and pop. Eh, no worries, I'll be alright with just doing the job myself, no charge."

-Deathstroke

--
Deathstroke is an assassin for hire and a supervillain that operates in various areas of the United States, but most significantly in Gotham City.

Deathstroke's real name is Slade Wilson, and as a young man, he was enrolled in the Military, until he volunteered himself for an experiment that was stated to turn men into super soldiers. The experiment completely failed, but not before Slade was injected with the serum. It increased his strength, speed and stamina, but also damaged him mentally.

Going home to his wife, Slade tried to get his family back together, when his wife refused, he attacked her, and was shot in his eye, leaving him half-blind. But his accident did not deter him from his job. Deathstroke is considered the world's greatest assassin, and is often hired to do big killing jobs without leaving a trace.

One of these jobs, were the parents of Tony Carter, whom Black Mask hired him to kill. He succeeded in killing them, but failed to murder Tony and his brother, who got away. His actions have put him into constant conflict with the entire Batfamily, but Tony Carter considers him his archnemesis. For he is the one who has brought him the most pain, by killing his girlfriend, Tony himself, and making his life constant hell.

With an incredible healing factor and deadly accuracy, Deathstroke may be impossible to fully take down for good.

Role in Events
Pre-Time Rip:

Before the events of the Time Rip, Slade Wilson became Deathstroke and killed the parents of Tony Carter.

The Time Rip:

Reliving his past, Tony Carter witnesses his first girlfriend's death at the hands of Deathstroke, and is unable to change these events due to Darkseid's rules. This causes Tony to get into an argument with Batman.

Pre- Arkham Knight:

Before the events of the Arkham Knight event, Deathstroke is believed dead, killed by Tony Carter.

The Arkham Knight:

Deathstroke appears in the Arkham Knight event, where he is a member of the Arkham Knight's army, luring Tony into a hostage situation. Shocked to learn he is alive, Carter fights him to a standstill. Tony eventually gets the upper hand and stabs Deathstroke in his good eye, permanently blinding him.