Mazie Keiko Hirono (born November 3, 1947) is an American lawyer and politician serving as the junior United States senator from Hawaii since 2013. A member of the Democratic Party, Hirono previously served as a member of the United States House of Representatives for Hawaii's 2nd congressional district from 2007 to 2013. Hirono also served as a member of the Hawaii House of Representatives from 1981 to 1995 and as Hawaii's tenth lieutenant governor from 1994 to 2002, under Ben Cayetano. She was the unsuccessful Democratic nominee for governor of Hawaii in 2002, defeated by Republican Linda Lingle in the general election.

Hirono is the first elected female senator from Hawaii, the first Asian-American woman elected to the Senate, the first U.S. senator born in Japan, and the nation's first Buddhist senator. She considers herself a non-practicing Buddhist and is often cited with Hank Johnson as the first Buddhist to serve in the United States Congress. She is also the third woman to be elected to Congress from Hawaii (after Patsy Mink and Pat Saiki).

In 2012, Hirono was the Democratic nominee for the U.S. Senate seat being vacated by the retirement of Daniel Akaka. Hirono won the election, defeating Lingle in a landslide, 63% to 37%. She was sworn in on January 3, 2013, by Vice President Joe Biden. Hirono was the only person of Asian ancestry serving in the U.S. Senate from 2013 until 2017, when senators Tammy Duckworth and Kamala Harris were sworn in, representing Illinois and California, respectively. Although Brian Schatz is Hawaii's senior senator because he joined the Senate a week before Hirono, following the death of Daniel Inouye, Hirono's three terms in the U.S. House of Representatives make her the dean, or longest-serving member overall, of Hawaii's congressional delegation.