Clock's secret identity was eventually revealed to be society man and former district attorney Brian O'Brien, whose background in college sports helped prepare him for heroism. As the Clock, he wore a three-piece suit, a fedora, and a black full-face mask (which was replaced by a domino mask years later). He usually left a calling card that bore an image of a clock and the words "The Clock Has Struck."
Brian O'Brien later went on to become the president of the United States of America. It was his idea to create a team of super-powered heroes that would be focused on fighting crime and wouldn't be reckless. This team became known as the Protectors.
The Character would be bought by Quality in 1940. When DC bought the rights to the Quality characters they did not renew the copyrights of the character and, thus, he fell into public domain. It would seem DC would not renew the copyrights decades later.
DC would make references to him in the Starman book. Shade would reveal through the Clock's journal that his death in 1944 was a great exaggeration and that he had been actively fighting crime in Chicago. Clock would become a founding member in JLA:Destiny. The book had many of the Quality characters as founding members or as villians.