Thomas I or Tommaso I (1178 – March 1, 1233) was Count of Savoy from 1189 - 1233. He was the son of Humbert III of Savoy and Beatrice of Viennois. His birth was seen as miraculous; his monkish father had despaired of having a male heir after three wives. Count Humbert sought counsel from St. Anthelm, who blessed Humbert three times, and it was seen as a prophecy come true when Thomas was born shortly after Anthelm himself died on June 26, 1178. He was named in honor of St. Thomas Becket.

Thomas possessed the martial abilities, energy, and brilliance that his father lacked, and Savoy enjoyed a golden age under his leadership. He had taken over effective rule of Savoy by August 1191, and despite his youth he began the push north-west into new territories. He conquerored Vaud, Bugey, and Carignano. He supported the Hohenstaufens, and was known as "Thomas the Ghibelline" due to his career as Imperial Vicar of Lombardy.

In 1195 he ambushed the party of Count William I of Geneva, which was escorting the count's daughter, Marguerite, to France for her intended wedding to King Philip II of France. Thomas carried off Marguerite and married her himself, producing some eight sons and six daughters.
1. Amedeo (Amadeus)
2. Umberto, d. between March and November 1223
3. Tommaso
4. Aimone, d. August 30, 1237, Lord of Chablais
5. Guglielmo, Bishop of Valence and Dean of Vienne
6. Amadeo of Savoy, Bishop of Maurienne
7. Pietro
8. Filippo
9. Bonifacio
10. Beatrice, d. 1265 or 1266, married in December 1219 to Ramon Berenguer IV, Count of Provence (1209-1245)
11. Alasia of Savoy, abbess of the monastery of St Pierre in Lyon
12. Ágatha of Savoy, abbess of the monastery of St Pierre in Lyon
13. Margherita of Savoy, d. 1273, married in 1218 to Hartmann I of Kyburg
14. Avita of Savoy, married Baldwin de Reviers, 8th Earl of Devon