If you want to see evil manifested in The Thorn Birds, look no further than the odious character of Luke O'Neill. Right from the start of his marriage to Meggie, this rough-hewn ranch-hand subjects her to a particularly cruel reign of domestic tyranny. It's clear from how Luke speaks to his new wife that he doesn't even regard her as an adult. In common with most men of his time and class, he sees women as little more than overgrown children who need to be kept firmly under the control of their menfolk.
That doesn't mean that Luke cares for Meggie like a child. On the contrary, he couldn't care less about her at all. He makes that crystal clear by leaving his wife behind while he goes off to make a bundle in the sugarcane fields. In the meantime, Meggie's expected to make ends meet by slaving away as a humble maid.
Luke's unpleasant nature is further in evidence when Meggie sends him a telegram informing him that she's given birth to their daughter. Instead of responding like a proud father would, Luke completely ignores the good news and doesn't even bother to reply. If we don't know it already, Luke is an entirely self-centered man who couldn't really give a hoot about another living soul.