Maegor III Targaryen

"Did you know that at one point Maegor the Third tried to outlaw it in the Seven Kingdoms? Wanted to arrest anyone caught charging interest and cut off both their hands."

- Mace Tyrell to Tycho Nestoris

Maegor III Targaryen is an unseen character in Game of Thrones. He is long dead by the time of the series. He was a King of the Targaryen dynasty.

Biography
At somepoint Maegor the Third tried to outlaw the practice of usury, and cut off both the hands of anyone caught charging interst on loans.

In the books
In the A Song of Ice and Fire novels, there is no such character. Indeed, there has never been any other member of House Targaryen named Maegor since the infamous "Maegor the Cruel", such was Maegor's repute that later members of the hose deliberately shunned the name.