Who is St. John from Catechism of the Catholic Church and what is their importance?

This Saint's name appears during a discussion of the Ten Commandments. In the arguments against stealing, this Saint explains that what people give to the poor belongs to them and is due to them. The gifts are not undeserved hand-outs, but to refuse them what they receive would indeed be unjust. This is a view which might not always be popular.