Sweyn sailing up the Thames. Sweyn Forkbeard (960 - February 3, 1014) was a king of Denmark (986-1014). Sweyn revolted against his father, Harald Bluetooth, and seized the throne. In 1000, with the allegiance of Trondejarl, Eric of Lade, Sweyn ruled most of Norway. Sweyn was involved in raids against England during 1002-05, 1006-07, and 1009-12. Some historians believe his invasion were motivated by the massacre of Danes in England ordered by Aethelred the Unready in 1002, in which his sister and brother-in-law were killed, but others argue that the main motivation for the raids was more likely the prospect of revenue. In 1013, he became the first Danish king of England. Cassell's Illustrated History of England, 1865 (cropped and cleaned).