Detailed Explanation
DEA Agent Hank Schrader was killed by Jack Welker, the leader of a neo-Nazi gang, in the devastating episode "Ozymandias" (Season 5, Episode 14). After Hank and his partner Gomez arrested Walter White in the desert, Jack's gang arrived for what was supposed to be a hit on Jesse Pinkman. A shootout ensued, killing Gomez. Despite Walter's desperate pleas and offer of $80 million to spare Hank, Jack executed him with a shot to the head. Hank's final words to Walt were: "You're the smartest guy I ever met, and you're too stupid to see—he made up his mind ten minutes ago." Walter's screams as Jack pulls the trigger remain one of the most gut-wrenching moments in television history.