He is a totally self absorbed relic of an ancient age. Goldberry, his River-daugher, is an old man's fantasy brought to substance and animation. He has everything the way he wants it and only takes interest in the Hobbits as an amusing curiousity. The Old Forest herded the company to Old Man Willow at his direction so that he could conveniently meet the one who would bring an end to his age.
Also, I'm going to have to find a new reference. The Encyclopedia of Arda doesn't have entries for The Green Dragon or The Ivy Bush but they do for the Golden Perch!