Homo erectus is an extinct member of the genus Homo of which humans, Homo sapiens, are the only surviving member. The Homo genus is the fourth of the great apes, other members being chimpanzees, gorillas, and orangutans, all part of the homonid family. Sometimes the word "human" is used interchangeably with the genus Homo, although the Homo erectus was certainly not a modern human. The species is called Erectus because of its upright posture and humanlike gait. Homo erectus lived between 1.8 million and about 500,000 years ago (but possibly as recently as 30,000 years ago), emerging in Africa and migrating as far as Southeast Asia.

Although Homo erectus is the longest-lived and most successful member of the genus aside from modern humans, it had a skull and brain only about 75% the size of ours. Otherwise, Homo erectus would look remarkably similar to a modern human, much more so than its chimpanzee-like predecessor, Homo habilis. Yet, it lacked the ability for complex speech, as shown by the analysis of the Turkana boy specimen found in Kenya in 1984.

Homo erectus was the first homonid to achieve many milestones: it was the first out of Africa and the first to use fire in a controlled way — albeit not routinely — possibly as long as 1.5 million years ago, although the earliest uncontroversial date is 300,000 BC. They were also the first seafarers, traveling to the islands of Southeast Asia. They had height similar to modern-day humans, and an extended childhood. Hunting was first made systematic by Homo erectus, and they pioneered the second major tool industry, symbolized by Acheulian handaxes, which are crafted by chipping away on both faces of the object. These were useful for scraping fat from carcasses. Homo erectus also made the first known kills of mammoths.

Most scholars believe that Homo sapiens is a direct descendant of Homo erectus, and others aren't so sure. Species considered more advanced than Homo erectus include Homo antecessor, H. heidelbergensis and H. neanderthalensis.