Haesten was a Danish warrior who served Erik and Sigefried. After the saxon rebellion in the city of Eoferwic (York) he has being captured and used in a show by Frisians. Uhtred freed him and accepted his oath of loyalty. Sly and self-interested, Haesten is a master of self-preservation and will do anything for the sake of personal gain.
Haesten is a historical person. He was a Viking chieftain from the 9th century known for his fierceness and cruelty. The norman chronicler Dudo of Saint-Quentin wrote about him:
'This was a man accursed: fierce, mightily cruel, and savage, pestilent, hostile, sombre, truculent, given to outrage, pestilent and untrustworthy, fickle and lawless. Death-dealing, uncouth, fertile in ruses, warmonger general, traitor, fomenter of evil, and double-dyeded dissimulator.'