In reality, Alec is not a d'Urberville at all; instead, his family was named Stoke, then Stoke-d'Urberville, and later just d'Urberville. His father had made a fortune in north England and had settled in the southern region of the island. He adopted a local name to blend in with the historical association of place.
Alec woos Tess with his suave talk and conspicuous wealth. Alec's motives are clear from the beginning: to seduce Tess for his own gain. It could be argued that even after seducing Tess, Alec does indeed fall in love with her and makes his plans to have her as his own a second time.
Alec is friendly at first, using his charms to lure Tess back to The Slopes for a second visit. When she returns to become the keeper of Mrs. d'Urberville's poultry collection, Alec uses scare tactics to force Tess to plead to him for relief. The wild ride to Trantridge in the cart is indicative that he will use any means to convince her of his power.
The scene of Tess' first visit, with Alec feeding Tess strawberries (Chapter 5) is very sensual and suggestive. A scene like this would have caused more than a few Victorian eyebrows to be raised. Hardy made a point to include such a scene early in the novel to pique the reader's response to the novel. Sex was not a usual subject for a book, and Hardy delivers in his first section lust, sex, and seduction.
Tess is no match for Alec. Whereas she is naïve and inexperienced, he is worldly and sophisticated. While she is burdened with the responsibility of providing for her family, he feels an obligation to no one but himself. Alec wears the young girl down to take advantage of her, but she continues to rebuff his advances at every opportunity. It is not until he rescues her from a fight, in Chapter 10, with other Trantridge workers that her fate is sealed. Sensing a chance to have Tess, Alec purposefully becomes lost in a trek through the woods. He rapes Tess while she sleeps awaiting his return.
Alec does not appear in Chapters 12-43. Nevertheless, we cannot say that he doesn't impact the story during these chapters. First, his earlier actions (specifically the rape) impact everything that follows. But his impact is not simply confined to the readers' understanding of the part he has played in Tess' current situation. Hardy brings Alec back to the story through Reverend Clare, who shares with his son (who later shares with Tess) Alec's conversion and ministry. Alec returns physically to the book in Chapter 44 as a street minister.
Alec is a "sunshine convert," renouncing his newfound faith as soon as he sees Tess again. Using twisted logic, Alec accuses Tess of causing him to stray from his ministry, "But you have been the means — the innocent means — of my backsliding, as they call it." He soon cannot suppress his passion for Tess, calling her a "temptress." Hardy notes that "The corpses of those old fitful passions which had lain inanimate amid the lines of his face ever since his reformation seemed to wake and come together as in a resurrection." Tess feels some guilt for Alec's plight, and he uses the situation to his advantage again, making her swear to leave him alone at a place called "Cross-in-Hand," the scene not of religious conversion, but of conversion to the ways of the dark side, with Satan. Cross-in-Hand is a symbol of evil, not good, "@'Tis a thing of ill-omen," Tess is warned.
Alec further lures the unsuspecting Tess by talking her out of remaining true to her marriage to Angel. He will not accept her rejection of him. He is relentless, and in Chapter 50, he is able to finally sway Tess by catering to her poor family. Alec takes full advantage of Tess at this point, and he convinces her to live with him as a d'Urberville. Thus, Alec has persuaded Tess to live a life of sin. This deception results in his death when Tess, enraged, stabs him.