OH 5 was discovered by Mary Leakey in FLK I on the morning of July 17, 1959.  While out on a walk she noticed a portion of a skull poking out of the ground [1][3]. It was located at 22 ft. below the upper limit of Bed I and was only visible because it was exposed by the erosion on the slopes. Louis Leakey published a summary of the find and context on August 15, 1959 in Nature. In this publication, Leakey proposed the scientific name Zinjanthropus boisei for the find. Zinjanthropus was derived from the word ‘Zinj’, which is the ancient name for East Africa, while boisei was in honor of Mr. Charles Boise one of their benefactors [4][1].  Since there is insufficient evidence to create a new taxonomic distinction, Zinjanthropus was eventually abandoned and replaced by Paranthropus boisei [5][6].

OH 5 is comprised of an almost complete cranium with the entire maxillary dentition. It was found as a single unit within the space of approximately one square foot by about six inches deep. Despite its fragmentary condition when found, the individual pieces of bone were in an excellent state of preservation, even fragile bones like the nasals were preserved [1]. The cranium is of an adolescent probably male, with an estimated age at death of 15-17 years [7][8]. 

The Leakeys nicknamed OH 5 “Dear Boy”, but it was also commonly called “Nutcracker Man” due to its large back teeth and jaws. Its cranium and mandible appear built to resist the stresses associated with heavy chewing and provide copious attachment areas for massive muscles of mastication [9][6].

OH 5 and other hominin fossils (e.g. OH 7 & OH 9) were previously stored in Nairobi, Kenya for decades. They have been successfully repatriated in 2008, and are now stored in the National Museum of Tanzania in Dar es Salaam [10].