The Gesta Danorum (Books I-IX) on Hather
The Danish History, > Book Eight.
attestation: Hather desired both the gold and vengeance for his father, so he agreed to slay Starkad
"Hather, desiring as much to enjoy the gold as to accomplish vengeance for his father, promised that he would comply with his prayer"
attestation: Hather beheaded Starkad, ending the life of the greatest champion in Danish legendary history
"But Hather, desiring as much to enjoy the gold as to accomplish vengeance for his father, promised that he would comply with his prayer, and would not refuse the reward."
attestation: Hather's father had been killed by Starkad, motivating his willingness to perform the deed
"vengeance for his father"