Crossword clue: who was the longest-serving senator in us history, serving from 1959 to 2010
2 answers found in Letterora's clue database (Wikidata facts, Open Trivia DB, WordNet and Webster definitions — all licensed sources).
Possible answers
byrd
4 letters
otdb
explorer and United States naval officer; led expeditions to explore Antarctica (1888-1957)
robert
6 letters
otdb
United States parliamentary authority and author (in 1876) of Robert's Rules of Order (1837-1923)