There Are several possible Companions added as the story progresses. You begin the game with Sean Mancer a fellow Technomancer and Zacharia's mentor. You can have two companions at a time. They will comment on the story.
Sean Mancer: Zachariah's mentor, he is your companion during the intiation quest that takes him from apprentice to full member. Leaves for the front lines against Aurora eventually put in charge of Camp 19 after disobeying orders and probably for speaking out one to many times about the path Abundance was taking.
Jeffrey Hunter: a soldier in Abundance's military.
Amelia Reacher: a Rover driver who is forced to help Zachariah escape, becomes a companion. A potential love interest.
Andrew Mancer: A techomancer apprentice who overloaded one day and lost most of his left arm. That incident was swept under the rug and he was exiled, everyone thought he died. He joins Zachariah in Noctis. Eventually Zachariah with Scott hook him up with a prosthetic allowing him to use his powers again. A potential love interest.
Phobos: A Mutant that Zachariah helps escape from Abundance's Mutant Pen, helped form the Mutant Nation.