Cotys I or Kotys I was born during the reign of Seuthes I.

He became king after he killed the previous Thracian king Hebryzelmis.

On gaining the Odrysian kingdom the Athenians makehim their ally.

In order to make his position stronger Cotys marries his daughter to the Athenian general Iphicrates who soon becomes the second person in command after the king.

Cotys assists the Hales, leader of Triballi, a powerful Thracian tribe of Moesia, against Abdera.

In 375 BCE, the Triballi rebel against his kingdom.

One of the reasons for this revolt is that the Triballi are unable to get luxurious goods and other items from the south.

Cotys stops the rebellion by rebuilding the Greek city of Pistiros.