A Japanese soldier didn't know WWII had ended and hid in the jungle for 28 years! Here's his story:

Shōichi Yokoi was a sergeant in the Imperial Japanese Army during WWII, and in 1943 he was transferred to the island of Guam. When Allied forces took the island the next year, Yokoi and ten of his fellow soldiers went into hiding. Over time his ten companions either left or died and Yokoi ended up spending the last eight years alone.

On January 24th, 1972, 27 years after the end of the war, Yokoi was discovered by two local men who were out checking their shrimp traps. Yokoi, who thought the war was still going, saw them as a threat and attacked them. Luckily they were able to subdue him without major injury. Yokoi had been living in an underground cave and used native plants to make clothes and bedding while getting his food by hunting at night. He had seen leaflets declaring the end of the war but believed them to be Allied propaganda.

Being able to survive that way for so long is a testament to his character. The only two Japanese soldiers to hold out longer than Yokoi were Second Lieutenant Hiroo Onoda and Private Teruo Nakamura.

Yokoi was so loyal to his country that after returning to Japan and visiting the Imperial Palace, Yokoi said "Your Majesties, I have returned home ... I deeply regret that I could not serve you well. The world has certainly changed, but my determination to serve you will never change." He never actually met the emperor.

(Source)