Who is in the trunk of the vehicle that Phil drives in the Hangover?

In "The Hangover," the character in the trunk of the vehicle that Phil drives is Doug Billings, the groom who goes missing during their trip to Las Vegas. The group initially forgets about him, leading to a series of misadventures as they try to retrace their steps and find him before the wedding. Doug's predicament adds to the film's comedic chaos and tension.