Avie Tevanian was a key player in the Mach research project at CMU, and when Jobs brought him onboard at NeXT, he made his work with Mach the basis of NeXTStep.

Avie Tevanian was a key player in the Mach research project at CMU, and when Jobs brought him onboard at NeXT, he made his work with Mach the basis of NeXTStep. When Apple bought NeXT, Tevanian became CTO as part of the reverse management takeover. The Mach version underlying Openstep was updated for OS X, but kept around since Tevanian was very much a Mach booster.