Zuckuss comes from the planet Gand, a species who honour the tradition and skills of bounty hunting. Zuckuss was one of the planet's most successful bounty hunters, or findsmen as the Gands call them. The findsmen were used mainly to find fugitive criminals and runaway slaves.
On their home planet, which is very gaseous, the Gands had established pocket colonies, all of which were ruled by a totalitarian monarchy. The findsmen were highly superstitious, and performed all their rituals rigidly so as to not make any errors. The sect of findsmen worshipped the swirling clouds of gases that hug over their planet. They held the belief that the mists above them would give them signs that would aid in the finding of their prey. But, as had happened on so many other planets, the Empire came to Gand, and imposed their far superior technology on the gas-breathing people, rendering their rituals and traditions obsolete.
This caused many of the findsmen to retire, but a few of the young ones decided to travel throughout the stars and carry on with the only profession they knew. One of these was the Gand Zuckuss. Bounty hunting had been in his family for generations, and he used many of the old rituals when hunting. He found he could use his intuition to find his quarry, and gained the name 'the uncanny one'.
When he was away from Gand, Zuckuss had to wear special apparatus to aid his breathing, as oxygen could kill him. Underneath his heavy cloak, he donned heavy armour, and slung a computer and sensor devices around his neck. This allowed him to go over any terrain or endure any environment in order to bag his bounty. He became famous, and so came into the service of Jabba. He worked for the big slug solo for quite a while, but was eventually paired up with 4-LOM, whose analytical skills worked perfectly with Zuckuss' hunting techniques.
They were in the grace of Jabba for a long time, but when they failed to catch Han Solo. They soon fell out of it. But Jabba was pleased to have Han, especially frozen in carbonite, and so let the pair off. To this day, the two bounty hunters keep alive the tradition of the findsmen, and are very successful at it, proving Imperial technology is not as good as good old rituals, and a bit of intuition.