Artaphernes the Younger was one of the defeated Persian commanders at the battle of Marathon (490 BC). He was the son of Artaphernes the Elder, half-brother of Darius I and satrap of Lydia during the Ionian Revolt. Artaphernes the Younger was thus the nephew of Darius.
In 492 Mardonius led an unsuccessful attack on Greece. A successful invasion of Macedonia and Thrace ended after his fleet suffered heavy damage in a storm.
In 490 Artaphernes the Younger and Datis the Mede commanded Darius's second attempt to punish Athens and Eretria for their part in the Ionian revolt. Artaphernes was the higher ranked on the two, but Datis the more able military man. Their army crossed the Aegean, taking Naxos on the way. They successfully captured Eretria, before crossing to the mainland. They then landed at Marathon, north-east of Athens, where they were defeated by the Athenian army (battle of Marathon, 490 BC).
Artaphernes survived the failure of the invasion, and in 480 BC when Xerxes carried out his own failed invasion of Greece, he commanded the Lydian and Mysian contingents in the Imperial army, although we don't have any details of his performance in this role.