Thomas Aquinas was born in southern Italy, at his father's castle, in 1224 or 1225 AD, just after the death of Francis of Assisi. Aquinas was from an even richer family than Francis: his mother was related to the Holy Roman Emperors, who ruled southern Italy at this time, and his uncle was the abbot (the leader) of the monastery at Monte Cassino founded by St. Benedict. Thomas Aquinas had an older brother who would inherit his father's castle and all of his farmland, so his father decided that when young Thomas grew up he should become the leader of the Monte Cassino monastery.
To teach him how to be an abbot, Thomas started school at the monastery when he was five years old. He studied there until he was ten, and then he went to study at the newly founded University of Naples, near his home (smart kids often went to college much younger then than we do now). But while Aquinas was at college, he met some radical students and professors who convinced him to change his plans.
These people, the Dominicans, wanted to build a Christianity that would be more pure and good - not concerned with money or power, the way the Popes were, but where the monks would really be poor, and they would devote their lives to study and to helping poor people. Aquinas - 16 years old - thought that sounded really exciting. He left Naples and started traveling to Rome, to become a Dominican monk (something like a Franciscan). His family was very upset, and his brothers actually kidnapped him on the way to Rome and dragged him back to his father's castle, where his father kept Aquinas locked up for more than a year to try to convince him to change his mind. Finally the Pope said Aquinas' father had to let him go, and Thomas Aquinas, now 17 years old, rode to Rome and became a Dominican monk.
The older Dominicans knew how smart Thomas Aquinas was, and after a couple of years, in 1244 AD, they sent him to study at a Dominican school in Cologne, Germany, with a famous teacher, Albertus Magnus (or Albert the Great). In Cologne, the other students made fun of Thomas for being so big and so quiet. They called him the Dumb Ox. But Albertus, his teacher, saw that Thomas was very smart. When Albertus decided to go work at the University of Paris, Aquinas went there with him. Aquinas ended up getting his doctorate from the University of Paris (where he met Roger Bacon), even though he had been involved in a long fight with the University about whether only professors at the University could legally teach in Paris, or whether other monks, not part of the University, would be allowed to teach (Aquinas took the side of the free teachers, who eventually won).
Thomas Aquinas spent the rest of his life traveling between Naples and Paris and Rome, preaching, writing, and helping to solve political and religious arguments as they came up. Dante heard Aquinas preach in Florence, and was very impressed. In 1274, while Aquinas was traveling on the Pope's business, he got sick and died at the monastery of Fossa Nuova. He was about fifty years old.