Meagher, Thomas Francis (1823–1867), an Irish rebel and United States army officer and political leader. He was born in Waterford, Ireland. A fiery orator, he advocated Irish independence, 1845–48, and was banished to Tasmania for high treason in 1849. He escaped in 1852 and came to the United States. During the Civil War he was a brigadier general, commanding New York's Irish Brigade.
In 1865 Meagher was appointed secretary of Montana Territory and took over as acting governor. Without authority he raised troops to fight Indians. In 1867 he disappeared from a Missouri River steamboat near Fort Benton. Murder was suspected, but investigators concluded Meagher fell overboard and was drowned.