His name was Gavrillo Princip (member of "The Black Hand"). My best friend in HS and I agreed this to be one of the most essoteric things we learned in History class. I knew it would come back to me someday (although I was hoping it would be during Final Jeopardy as I was going for my 5th win).
OMNI: Gavrillo had actually chickened out of the planned assasination attempt and strolled into a bar to drink. Archduke Ferdinand's motorcade, in a bizarre twist of fate, drove by the establishment where Gavrillo was drowning his sorrows. Opportunity knocked, and on second attempt, Gavrillo succeeded.