This the 'Lurtz (Newborn)' character, which can (as far as I can tell) only be unlocked by using the following code: QL28WB. NOTE: If you look at the character picker, there is one additional character available.
Once that is done the blacksmith character will be unlocked (you don't have to buy him), and the achievement should pop. You do this by crafting every singly Mithril item at the blacksmith (which also unlocks 'Here's a pretty thing!'). Once you've bought all the characters you will need to unlock one additional 'special' character for this achievement to pop. The easiest way to figure out where they are is to open up a Map Stone (or use 'View Map' from the pause menu), selecting the character you want to buy and then selecting 'Set Destination'. As you play through the story, characters are unlocked, and can be bought by going to their location in free-roam. For this achievement you need to unlock and buy all characters.
