After WWII, Hiroo Onada who is a Japanese officer, didn't surrender in 1945 and continued the war for 29 years because he didn't know the war was over.

From Wikipedia Hiroo Onoda (1922 - 2014).

Hiroo Onoda (born March 19, 1922) is a former Imperial Japanese Army intelligence officer who fought in World War II and did not surrender in 1945. In 1974 his former commander traveled from Japan to personally issue orders relieving him from duty. Onoda had spent almost 30 years holding out in the Philippines.

On February 20, 1974, Onoda was found by a Japanese man, Norio Suzuki ... Onoda still refused to surrender, saying that he was waiting for orders from a superior officer. Suzuki returned to Japan with photographs of himself and Onoda as proof of their encounter, and the Japanese government located Onoda's commanding officer, Major Yoshimi Taniguchi, who had since become a bookseller. He flew to Lubang where on March 9, 1974, he finally met with Onoda and fulfilled the promise made in 1944, "Whatever happens, we'll come back for you," ... Onoda was thus properly relieved of duty, and he surrendered. He turned over his sword, his Arisaka Type 99 rifle (in working order), 500 rounds of ammunition and several hand grenades, as well as the dagger his mother had given him in 1944 for protection.

Hiro Onoda passed away on January 16, 2014 at the age of 91 years.

Edited January 19, 2014.