The Steller sea lion is a large, near-threatened species of sea lion, predominantly found in the coastal marine habitats of the northeast Pacific Ocean and the Pacific Northwest regions of North America, from north-central California to Oregon, Washington and British Columbia to Alaska. Its range continues across the Northern Pacific and the Aleutian Islands, all the way to Kamchatka, Magadan Oblast, and the Sea of Okhotsk, south to Honshu's northern coastline. It is the sole member of the genus Eumetopias, and the largest of the so-called eared seals (Otariidae). Among pinnipeds, only the walrus and the two species of elephant seal are bigger. The species is named for the naturalist and explorer Georg Wilhelm Steller, who first described them in 1741. Steller sea lions have attracted considerable attention in recent decades, both from scientists and the general public, due to significant declines in their numbers over an extensive portion of their northern range, notably in Alaska.

The Aleutian Islands —also called the Aleut Islands, Aleutic Islands, or, before 1867, the Catherine Archipelago—are a chain of 14 main, larger volcanic islands and 55 smaller ones. Most of the Aleutian Islands belong to the U.S. state of Alaska, with the archipelago encompassing the Aleutians West Census Area and the Aleutians East Borough. The Commander Islands, located further to the west, belong to the Russian federal subject of Kamchatka Krai, of the Russian Far East. The islands form part of the Aleutian Arc of the Northern Pacific Ocean, and occupy a land area of 6,821 sq mi (17,666 km2) that extends westward roughly 1,200 mi (1,900 km) from the Alaskan Peninsula mainland, in the direction of the Kamchatka Peninsula; the archipelago acts as a border between the Bering Sea to the north and the Pacific Ocean to the south. Crossing longitude 180°, at which point east and west longitude end, the archipelago contains both the westernmost and easternmost parts of the United States, by longitude. The westernmost U.S. island, in real terms, however, is Attu Island, west of which runs the International Date Line. While nearly all of the archipelago is part of Alaska at the extreme western end, the small, geologically-related Commander Islands belong to Russia.