Was Ferdinand Magellan the first explorer to reach the pacific ocean?

Yes he was, Ferdinand Magellan, (1480 – 27 April 1521) was a Portuguese explorer. He was born in Sabrosa, in northern Portugal, and served King Charles I of Spain in search of a westward route to the "Spice Islands" (modern Maluku Islands in Indonesia).
Magellan's expedition of 1519–1522 became the first expedition to sail from the Atlantic Ocean into the Pacific Ocean (then named "peaceful sea" by Magellan; the passage being made via the Strait of Magellan), and the first to cross the Pacific. It also completed the first circumnavigation of the Earth, although Magellan himself did not complete the entire voyage, being killed during the Battle of Mactan in the Philippines.