Thor Heyerdahl was a Norwegian adventurer and ethnographer known for his notable transoceanic expeditions. He gained international fame in 1947 with the Kon-Tiki expedition, where he sailed 8,000 kilometers across the Pacific Ocean on a hand-built raft to demonstrate the possibility of prehistoric sea travel. Heyerdahl's theories challenged conventional thinking about ancient human migration, suggesting that early people could have made long sea voyages between distant cultures.