Lt. Hiroo Onoda heard many times that the war was over...he just didn’t believe it. He was part of a special infiltration unit deposited on Lubang Island late in the war, and they had been told to disregard any such reports as propaganda. Even when he and his men captured a modern Japanese transistor radio and were able to pick up Radio NHK out of Japan itself, they believed it was an elaborate plot...though they were quite interested in the race reports and news of the royal family.
In the end, Lt. Onoda finally surrendered when his old commanding officer—by then a bookshop owner in Tokyo, who had long since given Onoda up for dead—read him the Imperial order of surrender, in person.
Excellent documentary on this guy.