"Do I look like I enjoy being covered in white goo?"
In a word: Yes.
Madison is the Sinclair family tragedy. As an 09er, she shares their sense of entitlement and tries to fix the school election to favor the club. As something of a blonde bimbo, she unpleasantly lords it over her brighter, darker-haired younger sibling. That she was switched at birth with Mac Mackenzie makes the Mackenzies one of the luckiest families in Neptune.
She used to date Dick Casablancas but then moved on to Sheriff Don Lamb ("So what? She's 18. That's legal."), which proves that money and good taste don't always go hand in hand. But Madison is no prize herself — she spits in the drinks of people she doesn't like, and she has been known to write "slut" on cars because "whore" has too many letters. Too many for her to spell correctly, perhaps?
In Season Two, Madison enjoyed the sort of pleasing physical makeover that only a plastic surgeon can guarantee. She was obsessed with the size of her butt and Pep Squad pie. She and Gia were poised for a catfight over Dick...even though Madison eschewed his offer of quickies for the "longies" of older boys.
In Season Three, she got lucky. No, not that one — he's dead...sort of. No, Madison's Christmas trip to Aspen put her in the path of the self-destructive Logan Echolls. Logan had to hate himself to sleep with Madison, even if it did make him sick to his stomach. This is nothing compared to what it did to Veronica Mars, for whom Madison is the personification of everything she loathes and who can't shake the images of their union from her head. Madison nearly lost her brand new Merc for it. Logan lost the love of his life. Life sucks in Neptune.
Madison looks like a slightly used and skanky fairy princess with wonderful mountains and glitter on her nose. Pity she has no soul.
All bios: 3.12 3.11 2.16 2.13 2.07 1.21 1.11 1.06
Amanda Noret plays Madison Sinclair.