Who introduced and traded with indulgence?

Explanation

The indulgence is granted by the Catholic Church after the sinner has confessed and received absolution. The church had an abundance of good deeds carried out by saints that it wanted to sell. That way, these good deeds could benefit others for a sum of money that in turn could be used to finance big building works. This lead to trading in indulgence and absolution, but also protests, which ultimately led to the split of the church and the initiation of the Protestant Reformation.