(covers information from several alternate timelines)
This page contains information regarding Star Trek: Picard, and thus may contain spoilers.
A500s were not sentient (nor ever meant to be). They were capable of speech communication and following verbal instructions, but did not understand humor. Their biped Human design made them capable of all the basic locomotion, movement, and motor control of the typical organic (presumably something like using a ladder, for example), and had enough physical strength to tear titanium apart with their bare hands. It was likely that they all shared an identical, Human male appearance, and were only individualized and identified by a code stenciled on their forehead, consisting of a combined letter and number. (PIC: "Maps and Legends")
All A500 type synths shown on screen were portrayed by Alex Diehl.
The novel The Last Best Hope establishes that the A500 was created by Bruce Maddox and Estella Mackenzie at the behest of Geordi La Forge. The A500s were developed by combining Maddox's expertise in cybernetics with Mackenzie's work in bio-neural circuitry. They were not sentient and were designed to serve as a labor force for Utopia Planitia Fleet Yards' efforts to mass produce a fleet of transport ships to relocate Romulans and others threatened by the imminent supernova of the Romulan sun. They came online in late 2382 and were in mass production by 2383, with scores of A500s already beginning their work on Mars.