"Little Foot" is the oldest fossil hominid skeleton ever found in Southern Africa, the lead scientist examining the discovery said on Wednesday.
The skeleton is probably 3.6 million years old and is expected to help researchers understand our ancestors' appearance and movement.
"This is one of the most remarkable fossil discoveries made in the history of human origins research and it is a privilege to unveil a finding of this importance today", said Ron Clarke, the Wits University academic who discovered Little Foot.
Twenty years after the initial discovery, the process of excavation, cleaning, reconstruction, casting, imaging and analysis is complete, and researchers are ready to reveal Little Foot to the world.
Named "Little Foot", the skeleton was found about 40 kilometres outside Johannesburg by miners, blasting rocks inside the Sterkfontein caves.
"Our ancestors were standing up when they lived in the trees and when they came down they were standing up", said Ron Clarke, "Little Foot never went through the monkey stage, with long arms and long hands ".
Little Foot is relatively small, with a height of about 4 feet 4 inches.
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The specialised process of excavation then began in earnest right up until 2012, when the last visible elements were removed from the cave in blocks of breccia, a concrete-like rock. Within two days of starting their search in July 1997, they found what they were looking for.
This is the first time that a virtually complete skeleton of a pre-human ancestor from a South African cave has been excavated in the place where it was fossilised.
The results of the decades of studies will soon be released in a series of more than 25 scientific papers, the scientists involved say.
Professor Adam Habib, Vice-Chancellor and Principal of the University of the Witwatersrand says: "This is a landmark achievement for the global scientific community and South Africa's heritage".
According to National Geographic, a discovery of a large number of fossils at Malapa, South Africa in 2008 has helped the Cradle of Humankind theory along, though other scientists argue that East Africa might be a more likely origin point.
By placing the fossils at well over 3 million years old, Clarke is bound to reignite a debate about the age of the find, which has been disputed over the years.