Echmarcach mac Ragnaill was a dominant figure in the eleventh-century Irish Sea region. At his height, he reigned as king over Dublin, the Isles, and perhaps the Rhinns of Galloway. The precise identity of Echmarcach's father, Ragnall, is uncertain. One possibility is that this man was one of two eleventh-century rulers of Waterford. Another possibility is that Echmarcach's father was an early eleventh-century ruler of the Isles. If any of these identifications are correct, Echmarcach may have been a member of the Uí Ímair kindred.

The Kingdom of the Isles was a Norse-Gaelic kingdom comprising the Isle of Man, the Hebrides and the islands of the Clyde from the 9th to the 13th centuries AD. The islands were known to the Norsemen as the Suðreyjar, or "Southern Isles" as distinct from the Norðreyjar or Northern Isles of Orkney and Shetland. In Scottish Gaelic, the kingdom is known as Rìoghachd nan Eilean. The territory is sometimes called the Kingdom of Mann and the Isles, although only some of the later rulers claimed that title. The historical record is incomplete, and the kingdom was not a continuous entity throughout the entire period. At times the rulers were independent of external control, although for much of the period they had overlords in Norway, Ireland, England, Scotland or Orkney. At times there also appear to have been competing claims for all or parts of the territory. The islands have a total land area of over 8,300 square kilometres (3,205 sq mi) and extend for more than 500 kilometres (310 mi) from north to south.