Eppillus (Celtic: "little horse") was the name of a Roman client king of the Atrebates tribe of the British Iron Age. He appears to have ruled part of the territory that had previously been held by Commius, the Gaulish former ally of Julius Caesar who fled to Britain following the uprising of Vercingetorix, or possibly of his son. Eppillus is not mentioned in any historical sources. Coins bearing his name also bear the inscription COMMI.FILI which is generally read as Commios filius indicating at least a claim to be Commius's son.
After Commius's death in about 20 BC, based on numismatic evidence, Eppillus seems to have ruled jointly with another ruler named Tincomarus. The COMMI.FILI inscription also appears on Tincomarus's coins suggesting they could have been brothers.
In about 15 AD, Eppillus was succeeded as king of the Atrebates by Verica. Verica again issues coins with the COMMI.FILI inscription suggesting perhaps a third brother although Verica's possible presence in Rome in 47 AD would have required Commius to have lived a very long life.