Thomas Stewart Udall is an American diplomat, lawyer, and politician serving as the United States Ambassador to New Zealand and Samoa since 2021. A member of the Democratic Party, he served as a United States senator from New Mexico from 2009 to 2021. Udall also served as the U.S. representative for New Mexico's 3rd congressional district from 1999 to 2009 and New Mexico Attorney General from 1991 to 1999. Born in Tucson, Arizona to the Udall family, he is the son of former U.S. Representative and Secretary of the Interior Stewart Udall and the nephew of former U.S. Representative Mo Udall. His cousin is Mark Udall, who concurrently served alongside him in the Senate representing the neighboring state of Colorado.

New Mexico's 3rd congressional district serves the northern half of New Mexico, including the state's Capital, Santa Fe. The district has a significant Native American presence, encompassing most of the New Mexico portion of the Navajo Nation, situated in the northwest corner of the state, and most of the Puebloan peoples reservations. The current Representative is Democrat Teresa Leger Fernandez.