William Miles
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William M. is a member of the Assassin Order, who acted as a contact for the Assassin teams spread throughout the world. He regularly kept the teams informed about the situation of the others. The fact that he is privvy to senitive information suggests that he is a high-ranking assassin, though from the emails he sends to Shaun's laptop it is implied that he is not based at the Assassins' headquarters- though he is in regular contact with them.
For the Assassin team in Italy, he mainly relayed information through Shaun Hastings and requested him to forward it to the other members; for example he lets Shaun know about a possible disaster having occured to an assassin team in Denver, though he initially advises Shaun to keep this information from the rest of the Italian team. He also had a conversation with Lucy Stillman about the condition of Desmond Miles, who had been suffering from the bleeding effect, in which he said that they had to keep going, as they needed the location of the Apple of Eden.