Hero (or Heron) of Alexandria (c. 10–c. 70) was a Greek engineer and geometer. His most famous invention was the first documented steam engine, the aeolipile. He is said to have been a follower of the Atomists. Some of his ideas were derived from the works of Ctesibius.
A number of references mention dates around 150 BC, but these are inconsistent with the dates of his publications and inventions. This may be due to a misinterpretation of the phrase "first century".
The complete surviving works are
- Pneumatica (Greek, c. 60),
- Automata (Greek),
- Mechanics (Arabic),
- Metrics (Arabic),
- Dioptra (Arabic).
In optics, Hero proposed that light travels along the shortest geometric path. This view is no longer accepted, having been replaced by the least-time principle.
In geometry, he stated and proved a formula, now known as Heron's formula, for calculating the area of a triangle in terms of its sides. He also came up with an iterative process for calculating square roots of numbers.
Hero is credited with inventing many feedback control devices using water, fire and compressed air in various combinations, and the first type of analogue computer programming via intricate systems of geared spindles studded with pegs and wound with ropes connected to weights (trays of sand emptying over time) used to operate his automatic theaters that included automatic doors and multiple changing scenes of moving figures accompanied by lighting and sound effects.
- The Technology Museum of Thessaloniki has a good web page on Hero at 
- A translation of his 'Pneumatica' with diagrams can be found at 
- Michael Lahanas's page