The first Manticore was Justin Sinclair's father, who was killed by the villain known as Protean before his eyes. Watching them killed shattered Justin mentally, as his father tried to act the hero to the end: gambling the life of his innocent wife and his son. At first Justin was a rebel and troublemaker and did not want to become a Hero, but his fathers friend Michael White shaped him up. Eventually he became a Hero, but how this properly came to be has not been shown.
He has been shown to be arrogant and at times untrustworthy, a persona that he seems to encourage. He is a billionaire playboy and has turned his trust fund into developing an arsenal of trick arrows to combat his foes. He also founded Wyvern, sharing some of his trick arrow tech with them. At times he has shown himself to have an ego and seems self conscious of possessing no super powers, guardedly worrying that other heroes might look down on him for lacking powers. However during the comic books in the heat of one of the most dangerous battles of all he develops his super power: teleportation.
He is shown that unlike the rest of the Freedom Phalanx, he is willing to do whatever it takes to protect people and save lives: from breaking the law and killing, to sacrificing his life for others. This has strained his relationship with Statesman to the breaking point many times due to his going outside the law, but over time the two have developed a grudging respect for one another. This relationship was strengthened in steel when Manticore sacrificed his life to bring back Statesman.
On February 14th, 2008 Manticore and Sister Psyche got married, this event was mirrored in the City of Heroes MMO.