The Order of Preachers (Latin: Ordo Praedicatorum, hence the abbreviation OP used by members), more commonly known after the 15th century as the Dominican Order or Dominicans, is a Roman Catholic religious order founded by the Spanish priest Saint Dominic de Guzman in France and approved by Pope Honorius III (1216–27) on 22 December 1216. Membership in this "mendicant" order includes friars, nuns, active sisters, and lay or secular Dominicans (formerly known as tertiaries, though recently there has been a growing number of Associates, who are unrelated to the tertiaries) affiliated with the order. 

Founded to preach the Gospel and to combat heresy, the teaching activity of the order and its scholastic organization placed the Preachers in the forefront of the intellectual life of the Middle Ages. The order is famed for its intellectual tradition, having produced many leading theologians and philosophers. The Dominican Order is headed by the Master of the Order, who is currently Bruno Cadoré. Members of the order generally carry the letters O.P., standing for Ordinis Praedicatorum, meaning of the Order of Preachers, after their names.
What was one reason this group was founded?
to preach the Gospel