Who is Ikemefuna from No Longer at Ease and what is their importance?

Ikemefuna is a boy with whom Obi Okonkwo's father Isaac grows up, Ikemefuna is given to the Umuofians in appeasement and becomes inseparable from Isaac, but when the "Oracle of the Hills and the Caves" orders the boy killed, Isaac's father does it personally. Even then, some elders feel is is wrong to kill someone who calls one father.