Karna disguised himself as a brahmin to learn the mantra of a mighty weapon from this figure.  When he learned of the deception, he cursed Karna and would later fight on the side of the Pandavas as a result.  His own story begins when he kills an evil thousand-armed king but loses his parents in retaliation.  To gain revenge, he prays to Shiva, gets a mythical axe, and massacres 27 generations of Kshatriyas.  FTP, identify this sixth avatar of Vishnu, named for his weapon, the parashu.
Karna disguised himself as a brahmin to learn the mantra of a mighty weapon from this figure.  When he learned of the deception, he cursed Karna and would later fight on the side of the Pandavas as a result.  His own story begins when he kills an evil thousand-armed king but loses his parents in retaliation.  To gain revenge, he prays to Shiva, gets a mythical axe, and massacres 27 generations of Kshatriyas.  FTP, identify this sixth avatar of Vishnu, named for his weapon, the parashu.
Karna disguised himself as a brahmin to learn the mantra of a mighty weapon from this figure.  
Parashurama (prompt on "Rama of the axe")