12. Conrad Hilton
Showcase Episode: "Seven Twenty Three"
Based on the real-life hotel tycoon — Paris' great-grandpa — Connie Hilton meets Don on Derby Day, where they're both hiding from their hosts in an otherwise empty bar. This New Mexico cowpoke tyrant is the crustiest, funniest and just-plain-insanest of clients. He orders Don around, calls him at all hours, complains he doesn't have a Bible on his desk and takes no guff: "By golly, you're prickly!" Probably the only Mad Men character name-checked in a Pavement song ("Fin"), although "AT&T" could have been written about Don.