Wow—with friends like Lord Henry, who needs enemies?
This hedonistic, selfish aristocrat has the whole world at his fingertips, and, rather than doing something good for humanity, he simply goes about his business in a totally self-indulgent manner. Nothing seems to have any meaning for Lord Henry except his own pleasure:
"The only way to get rid of a temptation is to yield to it. Resist it, and your soul grows sick with longing for the things it has forbidden to itself, with desire for what its monstrous laws have made monstrous and unlawful. It has been said that the great events of the world take place in the brain. It is in the brain, and the brain only, that the great sins of the world take place also. You, Mr. Gray, you yourself, with your rose-red youth and your rose-white boyhood, you have had passions that have made you afraid, thoughts that have filled you with terror, day-dreams and sleeping dreams whose mere memory might stain your cheek with shame -- "
"Stop!" faltered Dorian Gray, "stop! you bewilder me. I don't know what to say. (2.8)
Even his so-called friends don't really matter to Henry once he's tired of them. For example, Basil, who's supposedly one of his best friends from university, disappears mysteriously for months at the end, but Henry doesn't even bat an eyelash. He's tired of Basil, and after all, the artist hasn't painted anything really good for a while. Basically, Henry's totally unfazed by the idea that Basil might be dead in a gutter somewhere; he doesn't even really think that's a possibility, since, in his view, Basil's too dull to be murdered. That is way harsh, Tai.
But that's just how Lord Henry views life. People, money, objects, art—everything is just a tool of pleasure to him:
Lord Henry went out to the garden and found Dorian Gray burying his face in the great cool lilac-blossoms, feverishly drinking in their perfume as if it had been wine. He came close to him and put his hand upon his shoulder. "You are quite right to do that," he murmured. "Nothing can cure the soul but the senses, just as nothing can cure the senses but the soul." [...]
"Yes," continued Lord Henry, "that is one of the great secrets of life—to cure the soul by means of the senses, and the senses by means of the soul. You are a wonderful creation. You know more than you think you know, just as you know less than you want to know." (2.14-15)
Once any given thing stops being fun, he's not interested any more. The one possible exception to this is Dorian himself. After years of "developing" Dorian's personality, Lord Henry feels as though he's created the ideal human being. He admires Dorian profoundly, but more importantly, he admires himself for having made Dorian what he is:
Talking to him was like playing upon an exquisite violin. He answered to every touch and thrill of the bow. . . . There was something terribly enthralling in the exercise of influence. No other activity was like it. To project one's soul into some gracious form, and let it tarry there for a moment; to hear one's own intellectual views echoed back to one with all the added music of passion and youth; to convey one's temperament into another as though it were a subtle fluid or a strange perfume: there was a real joy in that -- perhaps the most satisfying joy left to us in an age so limited and vulgar as our own, an age grossly carnal in its pleasures, and grossly common in its aims... (3.5)
All along, we see that Lord Henry and Dorian's friendship was nothing but a kind of science experiment; Lord Henry introduced a series of malicious elements to a pure subject, and watched their corruptive influence take hold. Since, in his mind, he molded Dorian in his own image, he doesn't think the other man can possibly ever change back.
And that's Henry's ultimate malicious triumph—he has created his own perfect companion, who is his equal (or better) in every way. The only thing Lord Henry neglected to foresee was the fatal intervention of conscience…but that's probably because he doesn't have one.