001 or Thanatos

He, his 3 friends and older brother are currently the top five in a group of assassins called the guild. The closer you are to 000 the better an assassin you are and the more you will get paid for each job. The higher your rank the less money the guild takes. To rank up, you kill whoever's rank you want. His skill is that he has a phographic memory. He retired but his spot as 001 still remains, and he holds a lot of the guilds secrets so they sent you and every non-hundred assassin after him.