Ex-husband of Naomi Nagata, Marco Inaros lives on Ceres Station. They had one child together during their marriage, Filip Inaros. Marco met Naomi when she was 16. She was doing classwork at Hygeia Station in the belt. Marco at the time was part of a mining and salvage crew that was working at Hygeia station.
The crew that Marco was working with was very pro OPA, not military yet, but they had all hated the inner planets. Marco is described as having dark eyes, soft dark hair, and to be very charming. People seemed to follow him. Naomi was taken by his charm. This all comes to an end when Marco leads and attack and destroys the Augustin Gamarra.
Unfortunately Naomi finds out that she actually, unwittingly helped in the ship's destruction. This event led to some very dark, emotionally unstable times for Naomi. She eventually breaks away from Marco and his company. Marco blackmails and threatens Naomi and keeps custody of Filip, against her vehement wishes. Seeing no option she leaves, both behind to start a new life. Marcos raises Filip on the belief that his mother was weak willed, and an enemy and traitor. He spins this story to his crew as well, and after years and years, it's ingrained in everyone.
Roughly 16 years since their split, Naomi is contacted by Marcos while the Rocinante is dry docked at Mars for major repairs that could take at least 2 to 3 months. Marcos asks her to put any differences they have aside and help their son Filip who is in trouble. She leaves Holden alone, and heads down to meet up with her old crew, Cyn, Karal, her son Fillip, and eventually Marco.
While it's true Filip was in trouble, (wanted for the attack on a Martian military site) Marco has formed a plot to kidnap Naomi and launch a sprawling attack on Earth, the Martian fleet, as well as the "main stream" OPA. His crew, including their son are all in on it, and succeed in imprisoning Naomi. It's revealed that for quite some time Marco and his crew have been launching raids, stealing equipment and abducting stray Martian ships as they cross through gateways. It was all leading up to a large counter strike against the "inners", and what would be an attempt at the assassination of the Martian Prime Minister Nathan Smith.
Marco releases a sort of press release to Earth and Mars stating his mission statement, basically recognizing the right for Earth and Mars to exist, but insists they must limit their spheres of influence to their respective planets. Belters, and more importantly his new "Free Navy" faction will control the gates and hence all intergateway travel. Taxes will be employed, and Earth and Mars will be on the hook for reparations for damages done to the OPA. The Free Navy, led by Marcos, will begin the long road to remaking humanity without greed or corruption that the inners are so fond of.
He wishes to close all gateway travel for now, and commandeer all colony ships and loot their goods to help build a strong Belt for the Free Navy. His speech about his demands, ideas and vision is more of a call to arms for all belters rather than just a mission statement.