Fox McCloud enters the series by going into a wormhole (Slipspace rift from Halo) with the Great Fox II months after the Angler Blitz without his friends. On the other side is what is simply called the Team Heretic Dinofox Universe, and here is where the main storyline is kicked off.
After the Great Fox II sustains major damage from not being graded for Slipspace travel, it exits the portal near a planet called Gauss Wisely. Fox could do nothing but watch as ROB desperately tried to stop it from falling into atmosphere. Without hardly anything to keep it from entering atmosphere, the Great Fox II fell into Gauss Wisely's hazardous environment; luckily it didn't disintegrate before hitting the surface and smashing to bits, and ROB as well as a few weapons were saved from the wreckage. Whatever was left of the GF II was sold in the Gauss Wisely's capital, in exchange for a starfighter FTL drive and a team to install it on Fox's Arwing II.
Fox goes on to fight the Chat Empire and forms a team called Team Heretic Dinofox, which includes Tyler Alshwind, Lord of the STARS, and Unnamed Field Marshall as the major members. Other followers include Drullkus, Yozoz, Trol' Lolam, and Nikolai Pereshenko. They are all terrorists in the eyes of the Chat Empire, but they are really fighting for freedom.
For almost all of the events in the universe, Fox is a major character.