What is "agathobulus"

Agathobulus (or Agathoboulos; 2nd century) of Alexandria, who lived c. 125 AD, was a Cynic philosopher and teacher of Demonax and Peregrinus Proteus.

Little is known about his life. In the Chronicle of Jerome, Agathobulus is ranked alongside Plutarch, Sextus and Oenomaus, as one of the principal philosophers flourishing in the 3rd year of Hadrian's reign (119 AD). According to Lucian, he was the teacher of Demonax; and Peregrinus Proteus studied the Cynic way of life in Alexandria under his tutelage:

Thereafter Peregrinus went away a third time, to Egypt, to visit Agathobulus, where he took that wonderful course of training in asceticism, shaving one half of his head, daubing his face with mud, and demonstrating what they call 'indifference' by erecting his shameful thing (aidoion) amid a thronging mob of bystanders, besides giving and taking blows on the rump with a rod, and playing the charlatan even more audaciously in many other ways.

This account should not be taken too seriously. Lucian disliked Cynics, and especially disliked Peregrinus.