Agents of STRIKE
Documented extranormal capabilities: Cage’s skin is difficult to penetrate, holding up against knives, bullets, industrial tools, and even high-temperature cutting torches. It also protects him against most blunt-force trauma, although things like a gun fired directly against the side of his head can give him a concussion. Cage also exhibits some degree of low-level superhuman strength, able to punch through walls and lift cars off the ground with some degree of effort.
Luke Cage was an inmate in federal prison when he was offered an opportunity to reduce his sentence if he agreed to participate in a Super-Soldier program that was being covertly operated at the time.
The program was illegal, and the inmates were not giving full informed consent to the procedure and were unaware of its potential side effects. Most of the test subjects died, went insane, or had horrific physical deformities. Luke alone had the desired outcomes, but only after an extended period of ill health as his body adjusted to the treatment. By the time he had manifested his abilities, the program had been uncovered and shut down, and Cage had been offered a pardon as an apology for his treatment.
Cage kept quiet about his abilities for years, and it was only in the last few years that SHIELD learned about him. He has been contacted and offered a position with both the Avengers and later STRIKE, and has declined both times to live as a private citizen. He does, on occasion, use his abilities to defend his neighborhood from criminal activities and he assists his girlfriend Jessica Jones in her casework, but he declines to conceal his identity or wear a costume while doing so.
SHIELD keeps a respectful distance from Cage and his activities, with the hopes that one day he can be persuaded to join the agency.