One of Ronald Reagan's nicknames. Reagan got the nickname from his film portrayal of Notre Dame football player George Gipp in the 1940 movie Knute Rockne, All American.
Reagan as Gipp gives a deathbed speech to his coach (Knute Rockne) saying, "Some day, when things are tough, maybe you can ask the boys to go in there and win just one for the Gipper." From that movie on Reagan was often referred to as 'the Gipper'.