a grand old man of

a (or the) grand old man of

a man long and highly respected in a particular field.
Recorded from 1882 , and popularly abbreviated as GOM, Grand Old Man was the nickname of the British statesman William Ewart Gladstone ( 1809–98 ), who went on to win his last election in 1892 at the age of eighty-three.
See also: grand, man, of, old