Jack

There are two characters who go by the name of Jack in the Metal Gear Universe.

Naked Snake, the main character of Metal Gear Solid 3: Snake Eater is referred to as Jack by his mentor, The Boss.

Jack is the real name of Raiden, the main character of Metal Gear Solid 2: Sons of Liberty. He is often called Jack by his girlfriend, Rose, and a few times by the game's antagonist, Solidus Snake.