The early Russian explorers named the islands by this term because of four prominent volcanoes, each located on a separate island. The Aleut name Unigun (Uniiĝun in the modern Aleut orthography) was reported in 1940 by Father Veniaminov.
There appears to be confusion regarding the names of these islands, possibly because only four of the five are on most early maps and charts. The present names were gathered in 1894 by a field party from  and published in 1895 by the U.S. Navy Hydrography Office (Chart 8).