Damien Darhk

Damien Darhk is the leader of H.I.V.E., and a former member of the League of Assassins. He was the best friend and former rival of Ra's al Ghul, as well as a former "Heir to the Demon".

Heir to the Demon
At one point, Damien Darhk and an unnamed man were horsemen of Ra's al Ghul. The former thought himself worthy of taking the mantle, though the latter was the chosen one. Damien was to be killed but managed to escape, taking with him waters of the Lazarus Pit and some loyal followers.

H.I.V.E.
According to Ra's, Damien in the present-day commands a "hive of followers" around the world. He tried to buy the earthquake machine from Milo Armitage then hired Gholem Qadir to release nerve gas in Markovia. Some time later, he also hired Mark Shaw to steal A.R.G.U.S. documents, but each of his attempts were met with failure.

In 2015, he visited Starling City. He was tracked down by Ra's al Ghul, but both Oliver Queen and he were too late to find him, instead leaving behind his assistant, who was killed by Ra's.

Personality
According to Ra's al Ghul, Damien is slightly arrogant and overconfident, as he believed himself to be the worthy successor to the then-Ra's al Ghul, he is intelligent and calculating, as he managed to stay ahead of Ra's for years, every time his best friend tried to kill him, according to his late assistant, he is not a person who can be caught off guard so easily.

Like most assassins, Damien is cold, ruthless and has a sense of honor.

Abilities

 * Genius-level intellect/Master tactician/Leader: Damien is able to lead a organisation in complete secrecy. He was able to  stay ahead and avoid both Ra's al Ghul and Oliver when they came for him.
 * Peak of human physical condition: As a highly skilled assassin, Damien would be in top physical condition.
 * League of Assassins training: Damien would have gone through the training all League members do. He likely possesses skills with a variety of other melee weapons such as swords.
 * Master hand-to-hand combatant/Martial artist: As a former Heir to the Demon and member of the League of Assassins, Damien is presumably a master in hand-to-hand combat and martial arts.
 * Master swordsman: Being a former member of the League of Assassins, Damien would likely be a master swordsman.
 * Master archer: Being a former member of the League of Assassins, Damien would likely be a master archer.

Behind the scenes

 * In the DC comics, Damien Darhk has connections with H.I.V.E., is a major target for the CIA and FBI and a villain for the super-hero team Titans. Damien acted as the second-in-command to Adeline Kane, Slade Wilson's ex-wife, and was responsible for reforming the H.I.V.E. into a more cohesive terrorist organization, as opposed to being a generic robe-wearing cabal.
 * In the DC comics, a character named Dr. Ebeneezer Darkk was the first person other than Ra's al Ghul to lead the League of Assassins.
 * Ironically, Doctor Darrk had a falling out with Ra's al Ghul, similar to the show's version of Damien Darhk, making it possible that the character is actually an amalgamation of the DC comic versions of Damien Darhk and Doctor Darrk.