Queen Isabella I was one of the most influential queens in history. Although she ruled together with her husband, King Ferdinand II of Aragon, it was Queen Isabella who encouraged and sponsored Christopher Columbus’s explorations. It has also been said of Queen Isabella that she was a gentle ruler and freed Native American Indians and slaves that Columbus brought back to Spain from his overseas travels.
But she is also known for the beginning of the Inquisition in Spain which expelled many Jews and Moors, so I don’t quite see how she could be considered a gentle ruler. On the plus side, she was a patron of scholars and artists.