Ulfilas (Ancient Greek: Οὐλφίλας; c. 311 – 383), known also as Wulfila(s) or Urphilas, was a 4th-century Gothic preacher of Cappadocian Greek descent. He was the apostle to the Gothic people.

Ulfila served as a bishop and missionary, participated in the Arian controversy, and is credited with converting the Goths to Christianity as well as overseeing translation of the Bible into the Gothic language. For the purpose of the translation he developed the Gothic alphabet, largely based on the Greek alphabet, as well as Latin and Runic characters. Although the translation of the text into Gothic has traditionally been ascribed to Ulfila, analysis of the text of the Gothic Bible indicates the involvement of a team of translators, possibly under his supervision.

Ulfila is mentioned by the Nicene Christians Socrates of Constantinople, Sozomen, and Theodoret, in addition to the Eunomian historian Philostorgius. He is also mentioned by the Gothic historian Jordanes, although the writer said comparatively little of him. The dominant and most important account of Ulfila's life comes from a 4th century letter from his pupil, Auxentius of Durostorum, who wrote it immediately after his death. A summary by Photios I of Philostorgius' Ecclesiastical History is also significant, but references to Ulfila's life are generally scarce, and he was omitted from Jerome's De Viris Illustribus.

Around the year 311, Ulfila was born presumably in what is now modern Romania. He was partially descended from Roman prisoners who were captured in a raid by Goths at Sadagolthina and carried away from Asia Minor. His ancestors were likely kidnapped by Western Goths in 264 or 267 then brought to an area near the Danube river. Prisoners taken in such raids from Anatolia were usually unrepentant Christians, and Ulfila was raised as a Christian in a pagan society. He lived in a diaspora community composed of Cappadocian Christians under the Thervingi between the Olt, Dniester, and Danube. It is believed that he was Cappadocian Greek on his maternal line and of Gothic descent through his father. Ulfila was either raised by Goths in his childhood as a captive or was born in captivity to Cappadocian parents.

No sources exist concerning Ulfila's education. However, he was a lector in a church in Gothia by age thirty, which required study of the Bible and prepared him as a translator. Since services were rendered in the Gothic language, he may have already had both the ability to translate and read. According to Philostorgius, he was sent by the Goths during the reign of Constantine I as an ambassador to the Roman Empire, where he was consecrated as the bishop of Gothia by the Arian Eusebius of Nicomedia. The Romans saw Ulfila as pontifex ipseque primas (bishop and tribal leader); Constantius II supposedly described him as the era's Moses and he was additionally compared to the prophet Elijah. His first journey to Constantinople was made between 332 and 337 for the purpose of accompanying a Gothic delegation, and he possibly lived in the city for a time with Aoric. His consecration took place in either 336 or 341.

Ulfila would master both Greek and Latin during his life, and as bishop he wrote theological and exegetical treatises in both languages. In 341, he returned to Gothia, spending the following seven years working to explain and confirm the doctrine of Arianism among existing adherents and the unconverted. His pursuits were abruptly ended in 348, when a Thervingian iudex began the persecution of Christians in the area. The exact catalyst of the persecution is unknown. Ulfila and his followers were expelled and fled to the Roman provinces, where they were accepted by Constantius II. Ulfila then established himself in the mountains near Nicopolis in Moesia Inferior, with no evidence that he would ever return north of the Danube. He had been the only religious and political leader of Christian Goths at the time of the expulsion, after which he held the honorary title of confessor. His followers were shepherds, and their descendants remained 200 years later in Nicopolis as a poor and docile community.

For 33 years Ulfila continued to serve as bishop and attended church councils. Little is known about his life in Moesia, but he resumed preaching and likely exercised the office of chorepiscopus (Greek: χώρα). Most of his theological works, including the translation of the Bible from Greek into Gothic, were likely to have been produced in this period. He seemed to have remained the temporal and spiritual leader of the Christian Goths in Nicopolis, possibly exerting influence beyond the Roman frontier into Gothia as well. He also engaged in theological debates and subscribed to Homoeanism, which became established at the 357 Council of Sirmium.

Ulfila was present at the Council of Constantinople in 360, where he endorsed the council's creed and represented the Moesian Goths as their leader. The Roman emperors during the tenure of his bishopric were generally sympathetic to Arianism, though the situation changed near the end of his life. In 380, Theodosius I issued a law against heresy, supported the First Council of Nicaea, and deposed the Arian Demophilus of Constantinople in favor of orthodoxy. The next year, he confiscated all church property belonging to heretics and banned all heterodox religious meetings. After the convocation of the Second Ecumenical Council, the Arian bishops Palladius of Ratiaria and Secundianus of Singidunum were anathematized. Ulfila would journey with them to Constantinople upon being ordered by Theodosius to attend a disputation. He likely traveled to the city in 383, although the emperor came to reject the Homoian position. Ulfila soon became ill, died, and was buried soon after, though not before drafting a creed affirming his belief in Homoianism. He was succeeded as bishop by the Gotho-Phrygian Selenas.