Hippodamus was the son of Herakles and Anthippe. Anthippe was one of the daughters of King Thespius. During his stay in the court of King Thespius Herakles impregnated 49 of 50 Thespius' daughters including Althippe who he lay with one night. The result of that particular encounter was Hippodamus.
Herakles & Anthippe
By Anthippe he [Herakles] had Hippodromus