The Archer of Black from Fate/Apocrypha, the trainer of Heroes, Chiron the centaur, er...well...he's not a centaur here. Chiron is pretty cool. You name a famous Greek hero, Chiron trained them. Hercules, Perseus, Achilles and many more. He acts like a teacher as well. His Noble Phantasms is one that can be used as long as the night sky is out with the only thing needed to activate it being a point of his finger. With Eye of the Mind being one of his skills he can out predict his opponent's actions. Those above him on my favorite servant list are there for more unique personalities and better stories.