To recap, the first four Masters of the Order of Preachers were:
After entering the Order of Preachers, Blessed Humbert was appointed as a Lector of Theology at the Dominican Priory in Lyon in 1226, and in 1237 he became prior of that monastery. Thereafter, in 1240, he was appointed as the Prior Provincial of Tuscany. In 1244, he returned to France and served as Prior Provincial there succeeding Hugh of Saint-Cher. Hugh left the position after he was made a Cardinal - the first Dominican Cardinal.
Then, in 1254, Blessed Humbert was elected as the Master General of the Order of Preachers. His initial work was the re-organization of the Order's Liturgy. He issued a new edition of the Order's Constitutions and he issued new Constitutions for all nuns. Blessed Humbert also instituted the collection of information on both St. Dominic and St. Peter of Verona with the intention of using these materials to seek both of their canonizations.
In 1255, he adjudicated a dispute on the Constitution of the Carthusians, and he would in the next year become the godfather of one of the children of St. Louis IX of France. Blessed Humbert further encouraged the missionary activities of his friars and he encouraged the schools in Spain to teach Oriental languages.
Under his period of rule, the Dominican Order flourished in Italy, Germany, Spain, France, and England. Humbert sent missionaries to the Greeks, Hungarians, Saracens, Armenians, Syrians, Ethiopians, and Tartars. He regulated the liturgy of the Divine Office, determined the suffrages of for the dead, commanded the history of the Order be recorded, and even issued minute decrees concerning the election of superiors, the reading of the Constitutions at meals, the transfer of friars from one house to another and other pertinent regulation. On the reorgnization of the Liturgy, Fr. Joret writes:
At the Paris Chapter of 1256, Humbert issued to the Order his annual encyclical in which he announced the completion of the liturgical reform. A monumental volume, a masterpiece of Parisian book production in the middle of the thirteenth century, was composed to be the model to which all copies must conform. Deposited at first in the College of St. Jacques de Paris, the most important house of the Order, it is to-day in Rome amongst the general archives of the Friars Preachers. Finally, in 1267 Clement VII gave his approval to our liturgy. Since then it has undergone no important modification. When Pius V in 1570 imposed on the entire Church the breviary and Roman missal, he made an exception for the liturgies which were more than two hundred years old. The Dominican liturgy was one of these.In 1263, largely on the account of his failing health, Blessed Humbert resigned his position as Master of the Order. On July 14, 1277, the holy Dominican Master passed from this life to the next. His feastday is July 14th. May he soon be declared a saint!
The Dominican Order as it currently exists owes much to the leadership of Blessed Humbert. One of the great hallmarks of the Dominican Order is its love and focus on studying. Blessed Humbert was instrumental in the focus on studying as he said, 'Our Order is the first to have thus linked study to the religious life, prius habuit studium cum religione conjunction" (Humbert, Opera, t. II, p. 29). Speaking of the Blessed Virgin, Humbert said, "Our Preacher never cease praising her, blessing her and preaching her when they preach her Son" (Humbert de Romans, Opera, Vol. II, p. 71).
For your edification, please consider reading the "Treatise on Preaching" as written by Blessed Humbert. The Text is available online by clicking here.