A master craftsman (sometimes called only master or grandmaster) was a member of a guild. In the European guild system, only master craftsmen were allowed to actually be members of the guild.
An aspiring master would have to pass through the career chain from apprentice to journeyman before he could be elected to become a master craftsman. He would often have to produce a sum of money and a masterpiece before he could actually join the guild. Becoming a master was often very hard.
In many guilds the master craftsman had strict obligations, one of which was to take on an apprentice (or several depending on the craft) to ensure the survival of the guild.
See the guild article for an in-depth description of the system.
