Mr. Wilcox is an Englishman through and through, with an upper lip so stiff you could use it as a cricket bat. He's the epitome of stoic, powerful, imperial manliness, which is why Margaret is so taken with him – and why her sister dislikes him so much for most of the novel. As a rich businessman with colonial ties (he runs some kind of rubber import business), we have to wonder exactly what Mr. Wilcox gets up to out in the world; as proved by the incident with Jacky in his past, it's not always morally correct.
It seems for most of the book that Mr. Wilcox has always been at a distance from his own feelings, and that he always will be. The only time that we see a crack in his façade in the early parts of the book is after his wife's death; he's deeply affected by the loss of Ruth, but he manages to pull himself together for the sake of his family and his business. He gets richer and richer as the novel proceeds, demonstrating what the narrator keeps emphasizing – people like the Wilcoxes are necessary for the smooth running of the world, and they will always prosper in it. He, like the race he represents, is hardworking, unemotional, and, in some ways, simply unthinking – he doesn't mess around with feelings, nor does he spend much time analyzing himself or his decisions. He's always living on a business schedule, and that doesn't leave much time for a personal life.
Until, that is, he falls for Margaret Schlegel. The marriage of Wilcox and Schlegel is the union of opposite poles; Margaret is all about the interior life, while Henry is meticulously separate from his own interiority and only cares about the exterior. It's Margaret's mission to change this. She sees the capability for deeper caring in Henry, and she vows to make him a "better man" by bringing him more in touch with his own feelings. It seems for a long time that she's not succeeding, for, even after the incident with the Basts at Evie's wedding, Mr. Wilcox can't entirely come to terms with the black spots on his own past. However, by the end, personal tragedy finally cuts through Henry's thick armor of brusque capability. After Charles's fate is decided, Mr. Wilcox breaks down for the first time, and by the end of the novel, he's softened into a more loving, understanding man.