The viking king that was killed by the trophy head he put on his saddle

Wikipedia:

Sigurd Eysteinsson (aka Sigurd the Mighty, ruled circa 875–892) was the second Viking Earl of Orkney, who succeeded his brother Rognvald Eysteinsson. He was a leader in the Viking conquest of what is now northern Scotland. Bizarrely, he was killed by the severed head of one his enemies, Máel Brigte, who may have been mórmaer of Moray. Sigurd strapped Máel Brigte's head to his saddle as a trophy of conquest, and as he rode, Máel Brigte's teeth grazed against Sigurd's leg. The wound became infected and Sigurd died.