IG-88 was a battle droid bounty hunter hired by Darth Vader to hunt down Han Solo.
The droid is mainly silver, with one part in orange. It is extremely similar in looks to the ordinary Assassin Droid.
IG-88 was a droid created by a group of scientists. However, the intelligence programs with which he was outfitted caused them to rebel, killing his creators. IG-88 boarded the Star Destroyer Executor and was hired by Darth Vader to hunt down The Millennium Falcon all away to Bespin. After the capture of Han Solo, IG-88 escaped with the bounty hunter, including Boba Fett onboard Boba's Slave I.
Appearances in Lego
One misconception is that IG-88 is an Elite Assassin Droid. IG-88 was one of the very first Assassin droids ever built, who escaped its owner's factory but not before causing it massive damage. After this IG-88 went on to become a bounty hunter.