Ashul Edwaru (아슐 에드와루) is the famed blacksmith, who created the 13 Month Series and is one of the master artisans (장인, jahng-in, lit. "craftsman") of the Tower. In terms of his position in the Gong Bang, he would be similar to a High Ranker.
He is also the author of the book "Of The Tower's Weapons". He starts the book by explaining that all weapons in the Tower are modeled after the weapons that Zahard and the 10 Great Warriors brought with them when they entered the Tower. This means that the weapons were originally designed for battle in a space filled with air or vacuum and not one filled with Shinsoo. All weapons, therefore, had to be redesigned to suit for use in Shinsoo. He ends by stating that understanding Shinsoo is essential if one wishes to understand weapons.
At some point Zahard gave to Ashul Edwaru the first half of the Key of the Tower. Ashul melted half of the key and turned them into the 13 Month Series, which Zahard made the princesses fight over them.
Notes and Trivia
Ashul Edwaru was born in the Tower and has lived in the Tower, even before Zahard and the 10 Great Warriors entered.
The 13 Month Series all have their names engraved on them. The engraving is in Japanese because their creator Ashul Edwaru uses a language based on Japanese. SIU made it clear there is no significance behind this, as Chinese, Arabic and other languages are also used throughout the manhwa.
Edwaru is second only to Macseth in weapons-craft.