Subject 617

Subject 617 is the main antagonist of the Half-Life 2 horror mod, The Hidden, where a squad of soldiers are hunted down by the titular monster.

Subject 617 is the product of an Infinitum Research science experiment in an attempt to enhance DNA. The outcome was a human twisted and mutated with basic superpowers, including superhuman strength, speed, agility, and invisibility. Subject 617 used these powers to escape, and a team of IRIS soldiers were sent in to assassinate it.

Trivia

 * The idea of a superpowered monster hunting down a squad of soldiers is an obvious homage to the Predator. One of the soldiers in The Hidden even reference a famous Predator quote.