Which explorer led the first expedition to circumnavigate the globe?

Magellan led it and did not complete it. He was killed in the Philippines in 1521, about halfway round, in a fight he had picked to impress a local ally. The expedition was finished by Juan Sebastian Elcano, who brought one ship, the Victoria, home to Spain in 1522 with 18 men aboard out of about 270 who had set out in five ships three years earlier.

The arithmetic of the voyage is brutal. Three ships lost, one deserted and sailed home, one mutiny suppressed with executions, and a Pacific crossing of three months and twenty days during which the crew ate leather stripped from the rigging and sawdust, and the survivors' gums swelled over their teeth with scurvy. The cargo of cloves that came back on the single surviving ship still turned a profit on the whole venture.

They also came home a day early by their own reckoning, which nobody expected. The ship's meticulously kept log said one date and Spain said another, because sailing westward round the world means seeing one fewer sunrise than someone standing still. It caused genuine consternation - a delegation was sent to the Pope about the missed religious observances - and it is the first practical demonstration of the problem that eventually produced the international date line.