Background
Jek once belonged to the Hek'kt clan, a small group of Jawas who scavenged and bartered their way across Daalang III. However, the life of a Jawa clan can be difficult even in the best of times and their tendency to not understand ideas like 'ownership' does them no favors. This became especially clear when the Hek'kt clan began stripping apart a Hutt's pleasure barge. The Hutt did not take this lightly.
Within a few hours, the Hek'kt Clan had been very nearly wiped out and their sandcrawler blown to pieces. Only Jek survived, hiding among the bodies of his fallen clan. Alone, afraid, Jek had little option but to find somewhere to shelter. He wandered for days until he reached a settlement, collapsing from exhaustion and dehydration. Most would have left the Jawa to his fate, unconcerned if another of the little rats perished. But fortune was with Jek as he fell outside Marshal Tamm's residence.
The Marshall wasn't a charitable sort, generally, but he wasn't about to leave some Jawa to die on his doorstep. He brought the creature to the local doc, got him some food and water, and made sure he was on the mend. Jek, with nothing left to him, no clan to return to, felt strangely indebted to the Marshal. Once he recovered, Jek swore an oath that he would serve Marshal Tamm to the best of his ability.
At first, this was mostly just running errands, gathering things for the man. Eventually, Jek ingratiated himself with the Marshal, and Tamm decided to teach him how to become an enforcer of the law. It was difficult going in the beginning. Jek, like many Jawas, had a hard time wrapping his head around some of the concepts like 'theft'. But he was committed to the cause and worked to become better.
Within a year, the Jawa was accompanying the Marshal when he went out to settle disputes and bring in lawbreakers. It was a very different life from what he had been used to, scavenging and scrapping, but it was uniquely fulfilling. And then the Marshal died. Jek knew it was a dangerous profession, but he had not been fully prepared for Tamm's demise. The man fell in a gunfight against a dangerous gangster, but took the thug with him. However, Jek was once again on his own.
His first instinct was to leave, to run, but that was not the way of the Marshal. Jek was scared, but he had also taken an oath. With little choice left, the Jawa took up the Marshal's blaster and now attempts to keep the peace in his very small corner of the galaxy.
Motivation
Cause (The Weak) - Jek knows all too well what it's like to be pushed around. A Jawa on his own makes for an easy target, but he has become a bit more able to protect himself. Now, he works to protect others who cannot protect themselves.