Born Jonathan Sazaki, he was just another human born and raised on Elysium. And, like many of his fellow colonists, he suffered through the devastation of the Blitz. In the wake of the recovery process, he stowed away on a departing relief aid freighter, bound for the asari colony of Lusia. "Anywhere is better than back there," - that was the mantra he kept repeating to himself the whole flight, all but falling out of his hiding place upon landing. Hungry and alone, the asari colonists took him in and arranged sanctuary at a nearby orphanage. Not long after, he was adopted out by an older Pureblood couple: D'Sani, a retired commando, and Maneena, a Matriarch and former political attaché.
As he grew and matured (kind of), Johnny learned the ways of the gun and general combat from D'Sani - who filled the "father" role of his parental couple - while Maneena (his "mother") stressed the usefulness of silver-tongued diplomacy. Both lessons came in handy when he decided, on his eighteenth birthday, to start a promising career as a freelance mercenary. He was given a decommissioned turian frigate, the Bangalore, and a tattoo of Athame's name in old asari scrit on his cheek as parting gifts (little fact: D'Sani did the inking herself). After the failed attempt to garnish business under the monicker of "Johnny THUNDERSTONE," he adopted his 'parents' name, M'Sonna. Business has picked up considerably since then.
It has been suggested that his unique mindset and mannerisms are dicectly caused by a as-yet diagnosed mental disorder, most likely induced by the stress and trauma of the Blitz.
Johnny's photoshopped appearance is based on images of Alec Newman.
A lot of Johnny's personality and mannerisms are inspired by Deadpool.