Ra's al Ghul

Ra's al Ghul (Arabic: رأس الغول‎ Raʾs al-Ġūl; "Demon's Head") is the leader of the League of Assassins. He is also the father of Nyssa al Ghul.

Season 2
In "Broken Dolls", Ra's sent a messenger to Sara Lance, ordering her return, though she refused and killed the messenger when he declined to report to Ra's that he had not found her, as she wanted.

In "League of Assassins", about a week later, he sent Al-Owal and a team of Assassins to bring Sara back by force, only to lose his team to both Sara and Oliver Queen.

In "The Scientist", Moira later contacted Ra's after Malcolm mentioned that he went to Nanda Parbat. It was revealed that Ra's wants to kill Malcolm for breaking the League's code of honor through The Undertaking.

In "Heir to the Demon", Ra's sent Nyssa and a team of League members to once again try to bring Sara Lance back to Nanda Parbat. It was revealed by Sara that sometime before the Undertaking, he released Malcolm Merlyn from his bonds to the League.

Trivia

 * Ra's al Ghul, along with his daughter, Nyssa, are normally portrayed as enemies of Batman and his associates. However, his organization, the League of Assassins, has a history with Green Arrow and Black Canary. In the comics Ra's' other daughter, Talia, generally has a higher profile, having been (briefly) married to Bruce Wayne and borne him a son, Damian.
 * It was revealed that Malcolm Merlyn was the only member Ra's ever allowed to leave the League, an act he seemingly regretted after Malcolm partially destroyed Starling City with a man-made earthquake.
 * In "Heir to the Demon", Oliver reveals that he has heard of Ra's al Ghul and the League of Assassins, and knows of his reputation. How Oliver learned this is currently unknown.