Leonty Andrianovich Gagemeister (Леонтий Андрианович Гагемейстер in Russian) (1780 — 1833) was a Russian seafarer and explorer of the Pacific Ocean, Captain of the 1st rank.

In 1806-1807, Gagemeister made a journey from Kronstadt to Russian America crossing the Atlantic, Indian and Pacific Oceans on his ship Neva. In 1808-1809, he explored the shores of Alaska and made trips to northern parts of the Pacific. In 1810, Gagemeister returned to St.Petersburg through Siberia. In 1812-1815, he was appointed chairman of the Admiralty of Irkutsk. They started building first ships for navigating across the Lake Baikal owing to Gagemeister. In 1816—1819, he was in charge of a ship Kutuzov, which belonged to the Russian-American Company. On this ship, he circumnavigated the globe for the first time with a stop in Russian America. In 1828-1839, Gagemeister made his second circumnavigation on a ship Krotky. During this journey, he discovered the Menshikov Atoll in a chain of the Marshall Islands and specified the location of some other islands.

An island and a strait in the Alaska region bear Gagemeister's name.