Homo neanderthalensis adult male - head model - Smithsonian Museum of Natural History - 2012-05-17
A model an adult Neanderthal male head and shoulders on display in the Hall of Human Origins in the Smithsonian Museum of Natural History in Washington, D.C.
Neanderthals are either a subspecies of Homo sapiens (Homo sapiens neanderthalensis) or a separate species (Homo neanderthalensis). It's not clear from the evidence.
Neanderthal lived between 350,000 and 24,000 years ago. It's not really clear who Neanderthal's ancestor was. It's possible it was Homo heidelbergensis, or Homo rhodesiensis (which itself may be a sub-species of Homo heidelbergensis).
Neanderthals interbred with early Homo sapiens about 80,000 and 50,000 years ago. Even today, a tiny percentage of the human genome in Europe is Neanderthal.
Neanderthals were discovered in the Engis Caves in now Belgium in 1829 by Philippe-Charles Schmerling.
Neanderthals were much stronger than modern humans and and only slightly shorter. Neanderthal brains are known to have been slightly smaller than a human brain at birth, but by the time they were adults their brains were slightly larger. They lived in large, complex social groups; used language; used fire; built buildings from animal bones and hides; and hunted animals in groups. For many years, scientists assumed that Neanderthals were carnivores, but there is evidence now that they gathered and cooked vegetables.