Eppillus (Celtic: "little horse") was the name of a Roman client king of the Atrebates tribe of the British Iron Age. He was the son of Commius, the Gaulish former ally of Julius Caesar who fled to Britain following the uprising of Vercingetorix, or possibly of his son.

After Commius's death in about 20 AD, based on numismatic evidence, Eppillus seems to have ruled jointly with his brother, Tincommius. Eppillus's capital was Noviomagus (Chichester) in the south of the kingdom, while Tincommius ruled from Calleva Atrebatum (Silchester Roman Town) in the north.

Eppillus became ruler of the whole territory a little before 7 AD, and Tincommius appears as a supplicant to the emperor Augustus in his Res Gestae, so he would seem to have been driven out in some sort of domestic intrigue. After this, Eppillus's coins are marked "Rex", indicating that he was recognised as king by Rome.

In about 15 AD Eppillus was succeeded as king of the Atrebates by another brother, Verica. At about the same time coins of the Cantiaci stamped with the name Eppillus start to appear in Kent, replacing those of Dubnovellaunus. It is possible that Eppillus was deposed by Verica, fled to Kent and established himself as king there, but equally possible that he was invited to become king by the Cantiaci, peacefully handing the rule of the Atrebates to his brother, or that he died and was succeeded by Verica, and that Eppillus of Kent was another man of the same name.