God Raises Up Saints in Crises

Here are a few:

St. Irenaeus—fought against Gnosticism

St. Francis de Sales—instrumental in turning 72,000 Calvinists back to Catholicism

St. Charles Borromeo—implemented the decrees of the Council of Trent  

St. Teresa of Ávila—reformer of the Carmelites  

Further reading:

Reform Yourself!: How to Pray, Find Peace, and Grow in Faith with the Saints of the Counter-Reformation.