Slade Wilson was sixteen years old when he first enlisted in the United States Army, having lied about his age. After serving a stint in Korea, he was later assigned to Camp Washington where he had been promoted to the rank of Major. In the early 1960s, he met Captain Adeline Kane who was tasked with training young soldiers in new fighting techniques in anticipation of brewing troubles taking place in Vietnam. Kane was amazed at how skilled Slade was and how quickly he adapted to modern conventions of warfare. She immediately fell in love with him, and realized that he was without a doubt the most able-bodied combatant she had ever encountered. She offered to privately train Slade in guerrilla warfare. In less than a year, Slade mastered every fighting form presented to him and was soon promoted to the rank of lieutenant colonel. Six months later, Adeline and he were married and she became pregnant with their first child. The war in Vietnam began to escalate and Slade was shipped overseas. In the war, his unit massacred a village, an event which sickened him. He was also rescued by SAS member Wintergreen, to whom he would later return the favor.
Chosen for a secret experiment, the Army imbued him with enhanced physical powers in an attempt to create metahuman super soldiers for the U.S. military. Deathstroke became a mercenary soon after the experiment when he defied orders and rescued his friend Wintergreen sent on a suicide mission by a commanding officer with a grudge. However, Slade kept this career secret from his family, even though his wife was an expert military combat instructor.
A criminal named the Jackal took his younger son Joseph Wilson hostage to force Slade to divulge the name of a client who had hired him as an assassin. Slade refused, claiming it was against his personal honor code. He attacked and killed the kidnappers at the rendezvous. Unfortunately, Joseph's throat was slashed by one of the criminals before Slade could prevent it, destroying Joseph's vocal cords and rendering him mute.
Slade Wilson's physical and mental attributes have been enhanced to superhuman levels as a result of the experimental serum he was given; he possesses heightened strength, agility, durability, and reflexes, and has the ability to utilize up to 90 percent of his brain capacity. Deathstroke also possesses a regenerative healing factor that enables him to recover from physical injury much more rapidly than a normal human; it does, however, have its limits, as it could not heal his missing eye nor can it regenerate entire limbs. This enhanced endurance enables him to survive otherwise fatal injuries, though recovering from such injuries renders him temporarily insane and ferociously animalistic. In addition to being a tactical genius with years of military experience, Deathstroke is an expert in many forms of unarmed combat and martial arts as well, serving as a master of Bōjutsu, Boxing, Jojutsu, Judo, Jujitsu, Karate, and Ninjutsu.
Deathstroke is highly proficient in the use of various firearms and melee weapons. He typically wields a wide variety of swords, including katanas, giant broadswords, and volatile Promethium-forged swords that can redistribute copious amounts of energy from any source directed against them. Deathstroke also utilizes a ballistic staff that fires energy blasts from both ends, though in more realism-focused versions, it fires bullets and miniature cannonball-like pellets instead. His staff can bend and stretch to adhere to his different martial art forms. Deathstroke's Promethium body armor is composed of a mesh-woven, kevlar chainlink mail capable of deflecting small arms fire. In the New 52, this armor is meshed with Nth Metal as well, allowing it to absorb blows from Lobo and Hawkman, although it could not withstand the power of Mazahs.