Gryphon is a founding member of the Knights.
Sometime around 4,000 BC, humanity became aware of the Gryphon, or he decided to adopt a human form. Either way, he entered the realm of public knowledge, though his ancient recorded exploits in Mesopotamia and later Greece have been interpreted in modern times as myths. His human form has had a variety of names throughout the ages (Tawaret; Anzu), though since Greek times he has preferred Niko(-medes, -laus, -demos).
The Gryphon is able to shapeshift from human to his true Gryphon form at will. The Gryphon appears as a giant lion with wings, and feet tipped with massive talons. He is immortal, magical, and merrily entertained by adventure. Out of boredom he likes to meddle in human affairs. He dislikes pettiness, criminality, lying, cheating, abuse, killing, and evil. So these things naturally drove him to join in the founding of the Knights at the beginning of World War II. It seemed to perfect way to pass another century or so.
Sadly, he was away on a personal mission in another dimension when the events of August 9, 1945 occurred. Several of his teammates were killed in an atomic bomb detonation set off by the villain Crimson Dragon. He hated that he missed that adventure and is sure he would have profoundly changed the outcome. Thus he vowed to stick around and help the team survive its future trials.