Lord Henry is Dorian's mentor, but certainly not in a good way – he's a poisoner of young minds and a teacher of evil. Before Henry languidly glides into the picture, Dorian is totally pure and innocent – he's a kind of untouched Bambi creature, who prances through life blissfully unaware of the evils of mankind. However, once Henry gets a hold of him, Dorian transforms almost instantly; his "unspotted" youth fades away, even though he still looks the same on the surface. To make things worse, Lord Henry also gives Dorian the accursed yellow book, which also has a profoundly malicious influence upon the morals of our young protagonist.
Lord Henry's true evil lies in the way he looks at other humans – not as equals, but as playthings. Even Dorian, his closest friend, starts out as a kind of experiment in perverse parenting; Lord Henry consciously sets out to "develop" Dorian more, and mold him into his own ideal: a totally hedonistic, eternally beautiful, amoral being.