The Master Assassins are the main villains of the limited series Ben 10 & The Master Assassins and they are one of the villains introduced in Crisis. They were originally lead by Leader.
Background
An evil entity that has existed as long as time itself influences a person to lead The Master Assassins. The first leader was chosen decades ago, and he was Azmuth. Azmuth founded the Master Assassins, and he regrets it. Other leaders include Leader and Ben Tennyson.
It is also revealed that entity does not make the choice for the leader. It gives a "suggestion" and if the person is willing enough to do it, then they will. This means Ben Tennyson turned evil out of his free will.
Crisis
Ben 10 & The Master Assassins[]
In Enter Assassins, The Master Assassins were introduced as assassins who can kill anyone. They murdered a group of plumbers and their next target is unknown. Ben, Rook, Kevin, and Gwen investigate a warehouse in which they believe is the assassins' headquarters, only to be proven wrong when a group of assassins lead by someone simply known as Leader. After being defeated, the assassins disappear. Before they disappeared, Leader informed Ben that the target is where they started. In a matter of minutes, Magister Patelliday was murdered by the assassins. At the end of the episode, Leader informs the assassins that their next target is Rad Dudesman.
In The Dudesman Theory, the assassins appeared to have killed Rad. However, the Leader later reveals that they only pretended to kill him in front of Ben to destroy his confidence. It is revealed that Rad escaped and his wehreabouts are unknown.
In The Hunt For The Illuminati, The Master Assassins kidnap Blukic and Driba because they know who their next target is. Blukic and Driba were meant to be dead, but an assassin convinces Leader to keep them as their scientists. Leader wants this to be kept a secret, so he kills the assassin.
In Breaking News, the assassins target Will Harangue. After distracting Ben, Leader kills Harangue through a sniper rifle from another building. Leader then reveals that the assassins plans were split into two phases. The first phase is to kill people to crush Ben's confidence, and the second phase is to kill people to get the "justice" they believe in.
In Real Targets, the assassins target Max Tennyson. Leader leaves the assassins to kill Max alone in this episode. For the first time since The Dudesman Theory, the assassins failed at killing their target and for the first time ever, Ben manages to successfully defeat assassins. The assassins also require a new member, and their top priority is to get Rook Blonko to join them.
In Right On Time, the assassins must stop anyone who gets in their way. Leader targets Professor Paradox. Rook, who's working as a mole, kills Paradox and escapes, making Ben think that Rook has been kidnapped.
In Guilty As Charged, the assassins targetted Azmuth. They killed him. It is also revealed that he is the first leader of the assassins. They also left Galvan Mark II for the dead.
Trivia
They are somewhat based off of the DC villains group, The League Of Assassins.
They are also based off of the main character of the show Arrow during season 1.
