Luke Cage originally named as Carl Lukas and engaged with petty crimes during his youth. She then quit with those activities during his adulthood to avoid his family being hurt by his actions. And so one of his friend named Stryker, planted a drug into his apartment where he was arrested and got jailed.Source here
image sourceDuring his imprisonment , he volunteered to an experient of Super-Soldier cell generation which was researched by Dr. Noah Burstein. And so he acquire the super power making his prison escape.
And so he did become a street hero along side with Spider-Man and Daredevil.