"One whom the dragons will speak with," he said, "that is a dragonlord, or at least that is the center of the matter. It's not a trick of mastering the dragons, as most people think. Dragons have no masters. The question is always the same, with a dragon: will he talk to you or will he eat you? If you can count upon his doing the former, and not doing the latter, why then you're a dragonlord."
Source: wiktionary