Thessalus (Ancient Greek Θεσσαλός, "Thessalian man"), also called Thettalus, was a son of Heracles and Chalciope who became king of Cos. Homer's Catalogue of Ships sends his sons Pheidippus and Antiphus with thirty ships from Cos, Calydnae, and Nisyros to Troy; later tradition sometimes makes him an eponym of Thessaly.
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I.Heraclid king of Cos
Apollodorus and Diodorus make Thessalus son of Heracles by Chalciope. After Carians settled Calydna and Nisyros, he took possession of those islands as well as Cos. His sons include Antiphus, Pheidippus, and — in some notes — Nesson.
In Iliad 2.676–680 the Coan contingent sails under Pheidippus and Antiphus, sons of Thessalus the Heraclid. The atlas id thessalus-cos is this island king, not Jason's son Thessalus of Iolcus, nor the Haemonid or Poseidonian eponyms listed under the same Wikipedia disambiguation.
II.Homonyms
Other Thessali include a son of Jason and Medea who becomes king of Iolcus; a son of Haemon; and a son of Poseidon linked to Minyas. Keep the Coan Heraclid distinct from those mainland eponym forks.