There are four Masters in the game. 
They are found both in your town map and in the Characters section. 

Their Character levels will determine the tier of items that you can craft. To increase their level you must upgrade the town buldings: 

• Garage for Will;
• Tailor Shop for Caroline;
• Workshop for Stanley;
• Laboratory for Irene. 

Masters gain experience from crafting items that are covered by their building.