His name was Fontaine Maury Maverick and he was a U.S. Congressman from Texas from 1935 to 1938. His grandfather signed the Texas Declaration of Independence. He was the leader of a block of New Deal progressives in Congress -- described by some sources as "maverick" congressmen -- but was defeated in the primary when he ran for a third term. Texas was a virtual one-party state at the time and the Democratic primary was pretty much the defacto general election. He was accused of being a communist during the primary campaign by members of the San Antonio Democratic machine. During his time in Congress he voted for an anti-lynching bill. This site also credits him with being instrumental in the defeat of bills that threatened civil liberties, as well as working to strengthen the Tennessee Valley Authority and helping to establish the National Cancer Institute.
In 1939, he was elected Mayor of San Antonio, crushing the political machine that had defeated him in his bid for a third term in the House. This contemporary report of the events indicates that he modeled his politics on New York's Fiorello LaGuardia. "The cardinal sin of liberals is letting their political fences sag. My election shows that progressives must be practical, understand their people, and have a strong political organization," he said. He held little truck for overarching political theories.
Defeated for reelection in 1941, he later held several positions in the FDR Administration during the war. He continued to work for progressive causes after his time in government ended, becoming famous as a lawyer willing to defend civil liberties.
His son, Maury Maverick, Jr. likewise was active in Texas politics, serving in the Texas legislature in the early 1950s, where he was known as a strong defender of civil rights. Later he worked for the ACLU, defending a bookstore owner accused of sedition for the titles he sold (Marx! Engels! Sartre!). The case went all the way to the Supreme Court.
Eventually he became a regular columnist for the San Antonio Express-News. Some of his columns are collected in this book.
Maury Maverick, Jr.'s great grandfather -- the one who signed the Texas Declaration of Independence -- refused to brand his cattle, giving rise to today's common usage: an independently minded person, someone who is his own man.
What does this have to do with John McCain? Almost nothing.