First you need to collect some runes. These can be found in many locations and will involve a battle to win the rune.
Once you have a collection of runes you can forge items with them in your citadel. Keep choosing various combinations of runes until you find one that will give you a god-like item. Win the mini game in order to forge the item and the achievement will be yours.
This achievement is probably the most difficult in the game.
Here is a guide for you: http://www.trueachievements.com/a12320/master-craftsman-achievement.htm
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