Human: In the movie, ‘Back in Time’, why did Doc Brown build the DeLorean time machine? Assistant: 
Doc Brown built the time machine to travel back in time to save his friend Marty McFly from being killed by a drunken George McFly. The DeLorean time machine was a time machine that could travel through time. It was powered by a plutonium-based flux capacitor, which was invented by Doc Brown.