Which explorer led the first expedition that sailed around the world?

The explorer who led the first expedition to sail around the world was Ferdinand Magellan.

Magellan commanded the Spanish expedition that departed in 1519 with five ships and roughly 270 men. Its original goal was to find a western route to the Spice Islands, now part of Indonesia, whose lucrative trade routes were contested by Spain and Portugal. The fleet crossed the Atlantic, passed through the strait now named for Magellan, and entered the Pacific Ocean in 1520.

The voyage was extraordinarily difficult. The Pacific crossing lasted about three months, and the crew faced hunger, scurvy, mutiny, storms, and conflict. Magellan was killed in the Philippines in April 1521 before the expedition was complete. After further losses, Juan Sebastián Elcano took command of the surviving ship Victoria and led it back to Spain in 1522.

This creates a useful distinction: Magellan led the expedition at its start, but Elcano completed the circumnavigation. Only 18 of the original crew returned with the Victoria. The voyage demonstrated on a practical scale that Earth could be circumnavigated and revealed the enormous size of the Pacific Ocean.