Reptile made his first appearance in the original Mortal Kombat as a hidden character. He was a combination between the original Sub-Zero and Scorpion characters. Mortal Kombat co-creators John Tobias and Ed Boon admitted in an interview that the "birth" of Reptile was when they took Sub Zero and Scorpion and fused the two into one and colored him green (yellow + blue = green). They decided to name the character "Reptile" because of his green color and their reference to lizards. In the original Mortal Kombat he did not have much depth, but in MKII he was developed into a full character with his own story and special moves.

Reptile is a saurian, which is a race of human-like reptiles. Although he is considered disgusting and hideous by most, he is highly revered for his stealth and loyalty. Reptile doesn't really want any power; his only goal is finding more members of his saurian race, and freeing Zaterra from Outworld. This goal is well meaning, but is has become obsession that has cost much of his sanity.
It is unknown exactly how old reptile is. Estimates run in the tens of thousands of years, or even millions. It is known that the Earthrealm was nearly destroyed by a battle between the gods millions of years ago. Reptile's race of saurians was forced to retreat to the realm Zaterra, but it was soon invaded by Shao Kahn. During the invasion most of the Zaterrans were killed in battle, and very few saurians were left. Among those, or among those descended from these survivors, was Reptile. Many others of his kind were forced into slavery, but Reptile was trained to be a servant of both Kahn and Shang Tsung. He has served as an assassin and personal protector for many masters, such as Shang Tsung, Shao Kahn, Shinnok, and Nitara. Although they failed to keep their promises of helping him he remains loyal, probably because Reptile seems to almost need a master and feels meaningless without one.

Reptile abilities come from many reptilian creatures. Although he is a saurian, Reptile remains mostly human in appearance. However, the mask and the skin behind is an illusion used to conceal his true lizard form. His saliva is made of powerful acid-like fluids that can easily burn right through most objects. Reptile is able to spit this acidic saliva at his opponents, which eats away at their flesh. He is also able to fire powerful homing blasts of energy. Reptile's greatest trait is his ability to change the pigments of his skin to mimic his surroundings, making himself completely invisible. Although saurians can disguise themselves as humans, the longer they are separated from one another, the more their human disguises degrade and vanish over time until their true forms are revealed. Not only does this affect the physical appearance, it also can affect the mind as well. saurians that lose their disguises completely will begin to regress into primal fits of blind rage, attacking anything that crosses his path.