Athanaricus (died 381) was king of several branches of the Thervings for at least two decades in the fourth century. His Gothic name, Athanareiks, means "Year King" or "King for the Year" and probably comes from the Gothic Athni meaning "year" and the Gothic Reiks meaning "king."

A probable rival of Fritigern, another Therving war chief, Athanaric made his first appearance in recorded history in 369, when he engaged in battle with the Eastern Roman Emperor Valens and ultimately negotiated a favorable peace for his people.

During his reign, the Thervings were divided by religious issues. Many of them had converted to Arian Christianity during the third and fourth centuries, but Athanaric continued to follow the old Germanic pagan religion. Fritigern, his rival, was an Arian and had the favor of Valens, who shared his religious beliefs.

Socrates Scholasticus, Sozomen, and Zosimus refer to conflicts between Fritigern and Athanaric. Ammianus Marcellinus and Philostorgius do not record such conflicts.

According to Socrates, Fritigern and Athanaric were rival leaders of the (Therving) Goths. As this rivalry grew into warfare, Athanaric gained the advantage, and Fritigern asked for Roman aid. The Emperor Valens and the Thracian field army intervened, Valens and Fritigern defeated Athanaric, and Fritigern converted to Christianity, following the same teachings as Valens followed. Sozomen follows Socrates' account.

According to Zosimus, Athanaric (Athomaricus) was the king of the Goths (Scythians). Sometime after their victory at Adrianople, and after the accession of Theodosius, Fritigern, Alatheus, and Saphrax moved north of the Danube and defeated Athanaric, before returning south of the Danube.

In 376, Valens permitted Fritigern's people to cross the Danube River and settle on Roman soil to avoid the Huns, who had recently conquered the Greuthungs and were now pressing the Thervings then living in Dacia. Athanaric's people were left to their fate, but many of them found their own way across the river, as well.

In 381, Athanaric unexpectedly came to the East Roman capital of Constantinople. According to Jordanes, he negotiated a peace with the new emperor, Theodosius I, that made some Thervings foederati, or official allies of Rome allowed to settle on Roman soil as a state within a state. Orosius (Historiae adversum paganos 7, 34) and Zosimus (New History 4, 34, 3-5) affirm this, but a more reliable source, Ammianus Marcellinus (Res gestae 27, 5, 10) tells us an entirely different story. According to him, Athanaric was banished by his fellow tribesmen and forced to seek asylum on the Roman territory. Cf. Themistius (oratio 15, 190-1), who likewise describes Athanaric as a supplicant and a refugee. Clearly, Athanaric was by then no authority to negotiate with; he was welcomed by Theodosius in Constantinople only because the Emperor wished to make a lasting impression on the Tervingi, who were still fighting the Romans.

A few weeks later, Athanaric died. A peace and a treaty with those Tervingi (or Visigoths), who still fought the Romans in Thrace, was concluded in 382 and it lasted until Theodosius' death in 395.