Henry I the Fat (French: Henri le Gros, Spanish: Enrique el Gordo) (c.1244–1274) was the count of Champagne and Brie (as Henry III) and king of Navarre from 1270 until his death in 1274.

He was born as the youngest son of Theobald I of Navarre and Champagne (who had in 1234 became King Theobald I of Navarre) and Margaret of Bourbon. In December 1270 Henry succeeded his eldest brother Theobald V of Champagne (Theobald II of Navarre) as King of Navarre and Count of Champagne.

His proclamation at Pamplona, however, did not take place till March of the following year, and his coronation was delayed until May 1273. After a brief reign, characterized, it is said, by dignity and talent, he died in July 1274, suffocated, according to the generally received accounts, by his own fat.

After his death with no male heir, the male line of the counts of Champagne and kings of Navarre became extinct.

In 1269 Henry married Blanche, daughter of Robert, Count of Artois, and niece of King Louis IX. He was succeeded by his only legitimate child, Joan I of Navarre; her 1284 marriage to Philip IV (who became King of France in the same year) united the crown of Navarre to that of France, with Champagne becoming part of the French royal domain.

In the Divine Comedy, Dante sees Henry sitting outside the gates of Purgatory, where he is grouped with a number of other European monarchs of the 13th century.