It’s an interesting writing decision that Mary Keay and Eric Delano are never referenced as sharing a last name despite being married. Of course, in real life there’s a thousand reasons why a couple might want to keep their last names, but from strictly from a writing and character analyst perspective I think the choice is really symbolic of how Eric was disconnected from his family.

One of Mary’s major goals is that she wants a legacy that rivals the Lucas family, yet her husband doesn’t share her last name. To me this symbolic of the fact that Eric was never really a part of the dynasty that Mary wanted to build. He might have envisioned himself as such, but there was always a difference between him and a Keay,

Mary always could have taken Eric’s last name as well. However, like I was just saying, one of the most important things to her was legacy, and in the end it was more important than her relationship with Eric.

Then we get to Gerard, who has Mary’s last name and a character arc that revolves around personal anatomy. He spends his life doing what his Mother figures want and never really finding a place in the world where he belongs before he dies. And I think him having Mary’s last name is a part of that tragedy. If he had his Eric’s last name then he would share the name with someone who wanted what was best for him. But since he has Mary’s last name he’s connected to a world of fears and a legacy that he never asked for.

So TLDR: Gerard having Mary’s last name ties into his themes of always being owned by someone. Eric NOT having Mary’s last name ties into his themes of never really being a part of her world, and Mary keeping her last name ties into her themes of wanting to intertwine her name to her the fears.