Ethan
Ethan is a Temporal Manipulation trainer. Initially he can be found in the South Gate Station cafeteria, after the blockade is lifted he's in Hanging Rat or Hardcore City Bar.
Player interactions
You can further dig his story through conversations in different bar, eventually discover that he use a Strange Medallion, made by his psi teacher, Avllin Kain, to cover his old age.
Ethan kill Kain to get back the medallion, failing to learn his final lesson.
You need enough Persuasion to take a look at the medallion. Insisting not give the medallion back will lead to the back story at first(need Intelligence), further decline will provoke a fight. If you pickpocket it from him without notice, then ask about it, he'll mad about missing it, suspecting everyone around then ask if you steal it. Showing it to him but refuse to return or deny stealing it will also provoke a fight.
If you return the medallion to him, he will then leave the map and disappear in a hurry.
After pickpocket it from him, his appearance and avatar will change to an old man.
Psionic trainer
Ethan can train Temporal Manipulation psi skills. In SGS, he can train woman character in two option places, one of which is in protagonist's private room.
He can teach Temporal Distortion, Psycho-temporal Dilation and Limited Temporal Increment if you have the required thought control skill level(and enough credits).