Unkar Plutt Is a powerful junk dealer on Jakku. At one point, he was the custodian of Rey before she set off on her own.
During his dealings, he came across the Millennium Falcon, unknowing its importance. This ship, which he stole from the Irving Boys, was in turn stolen from him by Rey, Finn, and BB-8 as they fled Jakku.
Chewbacca responds to this by ripping off one of Plutt's arms, putting any desires to reclaim the Falcon aside for the moment.