A “Corinthian” was a “Sporting Gentleman” of the Regency period (though the term was also used by Shakespeare)
The Corinthian was, above all, a sporting man. He drove his own horses, boxed, ride to hounds, shot and strove to be among the elite of this group would undertook these expensive as well as athletic endeavors.
They were also usually very particular about their dress, wearing the latest fashion.
Georgette Heyer wrote a novel called “The Corinthian” about such a dandy.
ETA hhat, according to OED, that uasage is derived from
“relating to the licentious manners of Corinth”