I would say Nightwing…or…Blue Beetle
I was going to say Blue Beetle, but I don’t know enough about the character to comfortably suggest him. But then she said she meant in terms of popularity and background. Therefore the obvious answer is Batman. Both are in a half-dozen books, and have a handful of books of characters originating from their own stories (Nightwing, Venom, Catwoman, Scarlet Spider, etc.).