How is Elesin Oba portrayed as a tragic hero?

A tragic hero is a hero who comes to a tragic end, usually death.  The hero does so in performance of his duty.  Elesin is the King’s Horseman in a small tribe in Nigeria during Word War II.   Like many cultures, Elesin’s tribe believes that there is an afterlife.  Elesin is honor-bound to commit suicide in order to keep his late king company.

Elesin says:

“Life is honour. It ends when honour ends.”

This sums up Elesin’s belief that his suicide is honorable and his duty.  In the end, Elesin is able to commit suicide, even if he does not do it as he intends.  He dies, and he dies doing his duty.