Shiv's husband Tom Wambsgans (played by Matthew Macfadyen) is deeply infatuated with the Roy family power and wealth, but remains an outsider. He does his best to fit in and earn the cruel patriarch Logan Roy's affection, but is instead constantly belittled, mocked, and thrown under the bus by his in-laws (and, often, his wife).
In an interview with Variety, Succession costume designer Michelle Matland explained how Tom's on-screen wardrobe reflects that outsider status. "He's just not an equal, on so many levels, to the people that he's competing with. It feels almost like a competition for him," Matland said. "And he's a very bright man. But he was not brought up in a household of great wealth. He was not educated the way they were. And so, he is a posturer. And there is a level of a facade on him where the clothes are, it's like Dressy Bessy, you know? It's laid on top of the person rather than worn organically like he owns it." Tom's boardroom style is, on paper, similar to Kendall and Roman Roy, but add on his "Dress Bessy" details of polished shoes, perfectly ironed shirts, gelled hair, and matching his tie to his pocket square. All those subtle details become an amalgamation that telegraph his otherness. Sure, he's wearing a suit but not like a Roy would wear a suit.
One "Tom" piece that neatly sums up Matland's point is the Moncler extra-puffy vest he wears in an episode that takes place inside a mountain top resort at a conference for billionaires. Puffy vests have, strangely, become symbols of power for businessmen, but in a sea of black padded vests, Tom's version is extra ostentatious. "One of the decisions that we made, for example, was when we did the big conference. There are eight million puffy vests in the world; his, of course, has to have the patch that says Moncler or whatever. He can't get past that because those identifiable markers on the price tags are the things that make him comfortable." By buying an expensive, flashy version of the puffy black vest, Tom thinks he'll fit in but, in reality, that try-hardness only makes him stand out more.
By the way, Matland does have a theory about the popularity of those vests on their white collar fans. She told The Ringer, "I think they wear them because they make them look tougher than they actually are. These are guys who never played football. The vests are something that make them feel bigger than they physically are."