Background
Jax was more crafted then born. From the depths of the Hutt Space, he was ordered to serve the hutt crimelord Geerda. The great Geerda had his own ambitions on expanding his clan's reach to the core world. Establishing his presence and forcing trade deals with the Republic, Geerda reached his ultimate goal by influencing economy and politics in Coruscant. Jax was one of his 'ambassadors' (practically enforcers) working on the Capital City Planet.
When the Sacking begun, Geerda acted vigilant. He ordered Jax to help at Jedi Temple, for which in return he expected a debt from the Order.
Little had known Geerda about Jax's true past. The young gank was meant to be one of the few chosen ones granted with freedom. But the authorities had been corrupted, and greedy for the syndicate credits, he was forced to become a cyborg and practically became a slave as well. Roughly brainwashed and emotionless, Jax preserved some of his past memories of the hope of freedom, and the lust for vengeance.
Motivation