From historical evidence we know that Thomas was tall, powerful man. The robustness of his physical person is proven by the very frequent and taxing journeys which he accepted, however much today one supposes that on some crossings he chose to go by river or by sea. There were, especially, his long trips on foot: from Naples to Rome, to Bologna, to Paris, to Cologne and back. (The laws of the Dominican Order prohibited the use of horses.) It seems he had a particular fear of lightning, perhaps from the memory of the death by lightning of his young sister.

Thomas was unmistakably heavy. An old student of his defined him as being very obese, bald, of dark complexion, with some tufts of blond hair. According to another witness he was cheerful with a gentle and affable disposition. He maintained the greatest rapport with his students, even to the point of inviting them to dinner to celebrate the recovery of his secretary, Father Reginald.

He was pious and faithful to the customs of the religious life. He celebrated Mass very quickly and attended another with devotion in order to commit himself in the first hour of the morning to teaching and, once the teaching was finished, to research and to writing his works surrounded by three or four secretaries. His proverbial distraction, which has been the inspiration of several anecdotes, was due to the complete immersion of his mind in intellectual speculation.

His immense literary production is explicable only by the presence and the help of the secretaries mentioned above. Sources speak of them and, according to eye witnesses, Thomas dictated to all of them at the same time. Dictation was the chief work of Thomas, the Master of theology. This, together with study until dark and holding to a rhythm and an intensity of study and scientific production, was truly impressive. The reason for the rarity of his autographs is because, rather than his legendary and illegible handwriting, Thomas conducted research in many fields of knowledge at the same time and had a great number of secretaries to record the output of his research.