Frank the Rabbit

Frank, also known as Frank the Rabbit, was a character in Donnie Darko.

Beginning
In the middle of the night, on October 2, 1988, Donnie is awakened from his sleep by a strange voice and led out onto a golf course where he converses with a life-size demonic-looking rabbit named Frank who tells him that the world will end in 28 days, 6 hours, 42 minutes and 12 seconds, Donnie then falls asleep after being told this. After waking up on the golf course the next morning, Donnie returns home to discover that a huge jet engine has fallen from the sky and into his bedroom. The next night Frank appears to Donnie and makes him flood his school.

Middle
Frank appears later on, tempting Donnie to do another thing, burning down the house of a motivational speaker, to which Donnie does, without hesitation. After burning down the house, Donnie finds Frank yet again at a movie theater, and questions him on why he "wears that stupid bunny suit," to which Frank replies "Why do wear that stupid man suit", this ends out in slightly heated argument, to which Frank vanishes. Frank appears again to Donnie in the mirror of his own bathroom, they converse about the world ending and Donnie tries to figure out how Frank's powers work, to which he gets no reply. When Donnies's sister comes in the bathroom, Frank vanishes. Later, when Donnie goes to a psychiatrist, he sees Frank again, who simply stares at him, freaking Donnie out, just to have Frank vanish again.

End
As a member of the manipulated dead, Frank's objective is to guide Donnie in his path to correcting the timeline of the primary universe by returning the jet engine to its original universe. It is revealed that Frank is Donnie's sister's boyfriend, who is shot in the eye by Donnie to avenge the death of Gretchen. At the end of the film, Donnie is able to return the jet engine to the primary universe as he witnesses the start of the collapse of the parallel universe in which the events of the last 28 days took place, and he himself is returned to October 2nd to wait for the jet engine to crush him. This shows that Frank was actually a beneficial force seeking to prevent the destruction of the universe.