"As your attorney I recommend you get a fast car with no top."
Tessek was a Quarren from the planet Mon Calamari. Though listed in official New Republic records as Jabba The Hutt's accountant, it's since been proven that these records are completely false in most ways. Tessek was a recovering alcoholic, who came to Jabba's Palace in search of help.
The Palace became his home quickly, as it was full of like minded people struggling to find the strength to overcome their various addictions. At Jabba's, they found that strength in numbers.
Tessek eventually was able to put himself through lawschool, and returned to Jabba's not as someone needing help, but as someone who could help others. He assisted anyone at the Palace in need of legal help, and even bailed Jabba out of a bind or two.
Tessek was visiting Jabba's Palace to go over the contract regarding Amanaman's biography of the Hutt, when a series of guests suddenly arrived. First two droids, then a bounty hunter who was actually a terrorist, and finally a psychotic Jedi. Jabba confided in Tessek his intense regret that he had to kill Luke Skywalker. Tessek understood though that the Jedi was a maniac who could never be rehabilitated.
They took Luke and his friends to the Sarlacc, but Luke went completely nuts and start killing everyone he possibly could. The rest were all murdered, including Tessek, when Skywalker blew the Sail Barge up.