There's no single navigator who definitively "proved" the Earth is round. The idea that the Earth is a sphere was around long before any circumnavigation!

Here's a breakdown:

* Ancient Greeks: Philosophers like Pythagoras and Aristotle proposed the Earth was round based on observations like the Earth's shadow during lunar eclipses and the changing positions of stars as one travels north or south.

* Early Circumnavigations: While explorers like Ferdinand Magellan (who died during the voyage) and Juan Sebastián Elcano (who completed the voyage) completed the first circumnavigation in the early 16th century, they didn't set out to prove the Earth was round. They were driven by exploration and trade.

* Eratosthenes: Around 240 BC, Eratosthenes, a Greek scholar, calculated the circumference of the Earth with remarkable accuracy. This was a significant step in understanding the Earth's shape.

So, it's more accurate to say that the Earth's roundness was understood through a gradual process of observation, deduction, and exploration.