Jedi master was the highest level of Jedihood that one could attain within the Jedi Order. To attain the rank, most Jedi Knights had to have fostered at least two youglings, in addition to having dabbled slightly in the Dark Side yet not have been swallowed up by it. Masters, as part of their schtick, claimed to be quite humble, but most were in fact highly powerful in the Force. Most Jedi Master were killed by the Empire during the Great Jedi Purge. How the Empire managed to achieve this eludes most historians, despite the vast amount of evidence.