Who was St. Dominic de Guzman?

You are referring to two, distinct individuals: St. Francis of Assisi and St. Dominic de Guzman. They knew each other and had met. Both were itinerant preachers who wandered the countryside preaching repentance and reform where ever they found an audience. Francis founded an order of friars that later became known as the Franciscans. Dominic founded an order of preachers later called the Dominicans (Order of Preachers).