The oldest possible human ancestor yet identified is Toumaï, known as Sahelanthropus tchadensis, who was collected from the Toros-Menalla locality of Chad, considerably west of the Rift Valley, where most of our ancient hominid ancestors have been discovered.
Cast of the Toumaï skull, taken at a conference by Michel Brunet at the University of Fribourg in Switzerland, 10 September 2008. Photo by Ludovic Péron
Toumaï died 7 million years ago, and his skull is the most complete Miocene ape yet discovered. With some debatable characteristics similar to the much-younger Australopithecenes (including possible bipedal locomotion), Toumaï is definitely a human ancestor you should know.