What is the relationship between Okonkwo and Ikemefuna in Things Fall Apart?

Ikemefuna is a boy who is taken as part of compensation for another village's tribesmen killing a woman of Umuofia in their market. Ikemefuna is taken care of by Okonkwo, and quickly becomes like a son to Okonkwo; Ikemefuna even calls Okonkwo father. Ikemefuna behaves like an ideal clansman, and becomes close to Nwoye, mentoring him as an older brother.

Eventually, Umuofia's elders consult with the oracle whom declares that Ikemefuna must die. Ikemefuna is led off outside the village and is struck with a machete. He speaks his last Words, saying "Father, they have killed me!" prompting Okonkwo to deliver the killing blow.