Dynastes is the son of Herakles and Erato who is one of the daughters of King Thespius. During his stay in the court of King Thespius, Herakles impregnated 49 out of the 50 of Thespius' daughters including Erato who he lay with one night. The result of that particular encounter was Dynastes.
"by Erato he [Herakles] had Dynastes"
- Apollodorus. The Library, 2.7.8.