Echmarcach mac Ragnaill was a mid 11th century Norse-Gaelic king who, at his height, ruled a kingdom which spanned the Irish Sea region, and included Dublin, at least part of the Isles (the Hebrides and Mann), and much of Galloway. The precise identity of Echmarcach's father, Ragnall, is uncertain. One possibility is that Ragnall was one of two early 11th century like-named rulers of Waterford. Another possibility is that Echmarcach's father was a particular early 11th century ruler of the Isles. If either of these identifications are correct, Echmarcach may have been a member of the Uí Ímair.
Echmarcach first appears on record in about 1031 or 1032, when he was one of three kings in northern Britain who submitted to Knútr Sveinnsson, King of Denmark, England, and Norway. Echmarcach is recorded to have ruled over Dublin from 1036–1038, and 1046–1052. After losing Dublin for the final time, he appears to have seated himself on Mann. About a decade later, in 1061, Echmarcach appears to have been expelled from Mann, and may have then fallen back into Galloway.
Echmarcach appears to have forged an alliance with the powerful Uí Briain. He may well have been the brother of Cacht ingen Ragnaill, wife of Donnchad mac Briain, King of Munster; furthermore, Echmarcach is recorded to have had a daughter who married one of Donnchad's Uí Briain kinsmen. Echmarcach's violent career brought him into bitter conflict with a branch of the Uí Ímair who had held Dublin periodically from the early 10th century. This branch was supported by the rising Uí Cheinnselaig, who finally drove Echmarcach out of Dublin (and likely Mann) once and for all.
In 1064, having witnessed much of his once expansive sea-kingdom fall into the hands of the Uí Cheinnselaig, Echmarcach accompanied (a then deposed) Donnchad upon a pilgrimage to Rome. Possibly aged about sixty-five at this point in his life, it was here that Echmarcach died, in either 1064 or 1065. On his death, an expatriate Irish monk appears to have styled Echmarcach "King of the Rhinns", in reference to what may have been his last holding, in Galloway.
Read more about Echmarcach Mac Ragnaill: Uncertain Parentage, Uí Briain Alliance, and Conquest of Dublin, Loss and Regain of Dublin, Manx Numismatics, and Possible Actions in Wales, Downfall in Dublin and Mann, Magnús and Ælfgar, Pilgrimage and Death in Rome, Margaðr and Guðormr