Coming from the world of Calamari, Tessek was a natural water breather, but he could also survive on land. He was a Quarren, a species who shared their water planet with the Mon Calamari. Together the species built huge cities which floated on the water. With their tentacles and mushroom-shaped heads, the Quarren acquired nicknames, such as 'squid heads'. At one time the peoples of Calamari had been enslaved by the Empire, but together they drove Palpatine and his minions away. They payed a huge price for their victory, for many beings had been killed, and a lot of the cities were utterly destroyed. Therefore many fled Calamari, hoping to find sanctuary among the stars.
So it was that Tessek flew away, and ended up on Tatooine. This was not ideal for a creature who needed regular water baths to survive, but in his employment he found a good job that would ensure he stayed alive. He became Jabba's accountant. Through this he was able to divert funds for himself, and he set up a nice little nest egg for when Jabba was gone. But he feared for his life, knowing that others in the palace had heard of his schemes. At one time he even set up an attempt on Jabba's life. The plan was that the Hutt would be killed by an Imperial inspection party, but the Hutt had already been informed of this plot, and opted for waiting for Tessek to make his next move. The Quarren was so furious and afraid that his plan had failed that when the messenger, a B'ommarr monk, came bearing the bad news, Tessek killed him instantly. His fears were realized when Luke came to the palace. Tessek wanted to escape, but Jabba had heard of his plots, and told the Quarren to come to the Sarlacc. As he was told this, he looked to Leia, who saw nothing but pleading in his eyes.
On the sail barge, Tessek once again looked to Leia, and saw in her face that a rescue attempt was about to be made. In the ensuing battle, Tessek managed to find a repulsor swoop, and escaped when the sail barge blew up. He flew back to the palace for his money, but the chaos there meant that it was impossible to do anything.
The past events came back to haunt him. The friends of the monk he had killed cornered him, and against his will laser-cut his brain out of his head and placed it in a nutrient jar. After all his plotting, Tessek was free of Jabba, and now had a whole lifetime devoted to thinking, free of the pleasures of the flesh.
