It was discovered in 1975 in Koobi Fora, Kenya, right next to Lake Turkana, in a survey led by Richard Leakey, by a field worker called Bernard Ngeneo.

[citation needed] KNM ER 3733 is one of the oldest Homo ergaster skulls in the world.

Recent research using magnetostratigraphy has determined the age of KNM-ER 3733 to be 1.63±0.15 million years old.

The features of KNM ER 3733 are less robust compared to the two male crania.

It is considered an adult because of the extensive wear of its teeth, the fact that its third molars were present before the individual died, and because its cranial sutures were fully fused, which is only possible in adult specimen.