Ammonius Saccas (; ; fl. 3rd century AD) was a Greek philosopher from Alexandria who was often referred to as one of the founders of Neoplatonism. He is mainly known as the teacher of Plotinus, whom he taught for eleven years from 232 to 243. He was undoubtedly the biggest influence on Plotinus in his development of Neoplatonism, although little is known about his own philosophical views. Later Christian writers stated that Ammonius was a Christian, but it is now generally assumed that there was a different Ammonius of Alexandria who wrote biblical texts.