Seuthes III was a King of Thrace c. 325 - 295 BCE. This coin was struck c. 305-295. AE 17.5 mm. 3.01 grams. Eagle standing right ΣEYΘOY above thunderbolt Sear Greek I --, page 171. It would follow 1725. Hoover HGC, Macedon 3.II 1715 "R2" "c. 305-295" The Kingdom of the Odrysian Thracians was annexed by Philip II in 342/1 BCE. However, in 325 when Alexander was far away toward India the region revolted and Seuthes III took the throne. In 323 Lysimachos recognized Seuthes as ruler of that part of Thrace. Seuthes seems to have still been on the throne at the end of the century, but further details of his reign are lacking. If you want a coin of every Greek king, it turns out there are a lot of obscure Greek kings!
That's a very appealing coin - I would like to get a Thracian king at some point! Well, I'm not sure what counts as obscure, but Evagoras I of Cyprus has a shorter Wikipedia page than Seuthes III, so maybe this coin counts! Evagoras I (411-373 BCE), 1/12 stater (0.93g, 11mm); Male head to r./Blank as made. SNG Copenhagen 42. Evagoras I took Athens' side against the Persians in the early 4th century BCE, but after the Athenians withdrew their support in 387 he was forced to become a Persian vassal. He was eventually murdered by a vengeful court eunuch. Isocrates describes him as a model ruler in his Panegyric.