Ambrogio Lorenzetti (c. 1290 - June 9, 1348) was an Italian painter of the Sienese school who was active from around 1317 until his death in 1348. His elder brother was the painter Pietro Lorenzetti. It is believed that they both died of bubonic plague in 1348.
The first evidence of the existence of the hourglass can be found in one of his paintings.
A portion of his painting The Allegory of Good Government was used as the cover illustration for the board game Siena.