What would one need to become to be called the best assassin? You will need to be able to kill someone without leaving any clue, or maybe leaving a single clue that would tell people that it was done by you, but they would never be able to prove it.
Alex was once just like that.
He was trained to be the best since the tender age of 9, a year after his family died.
After that, from the age of 12, he started going on missions alone and in groups. He wasn't accepted by many people, as all of them thought of him as a weak 12-year-old child, but he didn't care.
He grew and grew until he reached the age of 12. That was when he had reached the best he could, a point where he was among the top assassins in the world.
No one knew his real name, nor did they know his face; all they knew was the black and white mask he used to wear and his trademark sign—a cross made of his target's blood.