Óengus II

Óengus mac Fergusa (variants Onuist, Hungus or Angus) was king of the Picts, in modern Scotland, from 820 until 834. Tradition associates him with the cult of Saint Andrew and the Flag of Scotland.
Óengus succeeded his brother Caustantín to the throne. Previously thought to have been of Dál Riatan origin and descended from Fergus mac Echdach, their family is now assumed to have been that of the first king Óengus mac Fergusa, perhaps originating in Circinn (presumed to correspond with the modern Mearns), a Pictish family with ties to the Eóganachta of Munster in Ireland.
Óengus, along with his brother, son Eogán, and nephew Domnall, is included in the Duan Albanach, a praise poem from the reign of Máel Coluim (III) mac Donnchada listing Máel Coluim's predecessors as kings of Scots, of Alba and of Dál Riata from Fergus Mór and his brothers onwards. The inclusion of Pictish kings from Caustantín to Eogán in the Duan led to the supposition that Dál Riata was ruled by Pictish kings, or rather that Dál Riata kings ruled Pictland, leading to supposition that the origins of the Kingdom of Alba lay in a Gaelic conquest of Pictland. However, it is now suggested that their inclusion is due to their importance in the religious communities of Dunkeld and St Andrews, where they were seen as founders and early patrons. However, a modern reconstruction of the later lists of Dál Riata kings presumes that Óengus's nephew Domnall was king of Dál Riata during this time (approximately 811–835).
Óengus's connection to the Saltire, set out at length by later chroniclers such as John of Fordun and Andrew of Wyntoun, comes from an earlier source, the older St Andrews foundation legend, which appears to date from the 12th century or before. The simplest version, stripped of the vivid, and probably misleading, detail added by later chroniclers, has "King Hungus" and his army win a victory aided by Saint Andrew, in gratitude for which the Picts agree to venerate the Saint. The name of their enemy may, or may not, be Athelstan, but this is most unlikely to be either of the English kings, nor the Viking convert, who shared that name.
The religious site at St Andrews, originally Cennrígmonaid, long predates this Óengus. Túathalán, first known Abbot of Cennrígmonaid, died in 747, and it is thought likely that the establishment is due to the earlier Óengus (king from 729; died 761) or to Nechtan mac Der-Ilei (king 706–724 and ?728–729; died 732). The St Andrews Sarcophagus is assumed to have been made for the remains of Nechtan or the first Óengus. The later St Andrews tradition recounting the supposed arrival of Saint Regulus (or Saint Rule) at St Andrews, with relics of St Andrew, has him met at Forteviot by three sons of Óengus: Eogán, Nechtan and Finguine.
Óengus died in 834, the only event of his reign reported in the Irish annals, and was succeeded by his nephew Drest mac Caustantín. Óengus's son Eogán was later king and was killed with his brother Bran in a battle against Vikings in 839.