Epictetus was a 1st century Roman Stoic Philosopher. He was extremely influential in his time, both in popular Roman culture and morality, and philosophy. Epictetus was born a slave and lived a very rough life. His leg was crippled from a young age, supposedly from his master punishing him. He also struggled with illness his entire life, however eventually he was able to become a free man and establish a school of philosophy, where he taught until he died. While I'm not sure there are any account of what type of teacher he was, due to the harsh, demanding style of his Stoic ethics it isn't hard to imagine that he might have been demanding of his students (or perhaps not, but that's at least how I imagine it).
According to his philosophy everything happens according to nature. So, according to Epictetus, it is simply irrational to get upset at things being as they are. He rejects that external events can cause in us negative feelings, and instead claims that it is our attitudes and judgments of those events that cause suffering. So, if one is to cry over spilt milk, it isn't the milk that made us cry, but our own belief that it shouldn't have spilled. Once we recognize that the milk spilling is in perfect accord with the predetermined harmony of the world, well then I guess it shouldn't bother us. Realizing how difficult this kind of life was for most people, he also had practical advise on how to achieve the stoic frame of mind. For example, he said that we should visualize negative outcomes ahead of time (such as a loved one dying), to mentally prepare ourselves for their inevitable arrival.
You can find out more about Epictetus on the History of Philosophy without any Gaps, or Partially Examined Life (the linked article is pretty informative too).