Barbarosa
(1982)

Karl (Gary Busey), a farmhand, accidentally kills his brother in law.  The man's family want revenge, and Karl flees into the desert.  Karl meets Barbarosa (Willie Nelson), an outlaw.  Barbarosa teaches him to survive in the wild.  Barbarosa is married to a Mexican lady, who lives on her father's hacienda with her large extended family.  Her father has sworn to have Barbarosa killed, even though the daughter loves him.  The father keeps sending young men after Barbarosa, even though Barbarosa kills them all.

Eduardo stabs Barbarosa.  As he lies dying, Barbarosa asks Karl to hide his body, so they will never be sure he is dead.  Barbarosa wants the clan to consume their lives searching for him, even after his death.  Karl pledges to kill Eduardo, so they will never get news of Barbarosa's death.  Eduardo reaches home first.

There is a fiesta to crown Eduardo heir to the family.  Karl dresses as Barbarosa.  He rides through the fiesta shooting it up, and steals the crown of flowers.

The family thinks Barbarosa still lives. 

Thanks Joseph C!