Great hackers can't reliably rank themselves, and outsiders can't see the difference at all — you can only tell by working with someone. So this site asks the only people who'd know: other hackers. You name the best hacker you've ever worked with. They, in turn, name theirs. Follow the chains, and the names that keep getting nominated start to surface.
“Because you can't tell a great hacker except by working with him, hackers themselves can't tell how good they are.” — Paul Graham
“If there is a Michael Jordan of hacking, no one knows, including him.” — Paul Graham
Done. Send this to the person you nominated — their name will already be in the “Your name” field so they can pass it on:
Local maxima — people nominated as best, who haven't yet named someone better. Counts include transitive nominations: if A → B → C, then C has 2.