It was during the middle 1880’s that Republicans started calling themselves the G.O.P. for Grand Old Party.
It was apparently adopted from grand Old Man, the nickname of England’s William Ewart Gladstone, one of the most popular and powerful men of his time.
Democrats first used the term as a taunt but over the year, G.O.P. has come into common and widespread usage, without regard to meaning and is especially utilized by newspaper headline writers because of its shortness.