Atoq Navarro led a group of highly trained South American mercenaries. They, along with the archaeologist, were hired by Gabriel Roman to serve as security in the search for El Dorado. They were the most common enemies of Nathan Drake in Uncharted: Drake's Fortune during his search for the fabled gold, sent patrolling constantly to eliminate him.
At some point, Gabriel Roman approached Atoq Navarro, an archaeologist with knowledge of El Dorado, in a slum in South America. Roman was aware that his rival, Victor Sullivan, was close to finding the treasure along with his good friend, Nathan Drake. Roman wanted compensation for money Sully owed him. He needed to hire soldiers to help his excavation of El Dorado, and someone with knowledge of the treasure's history. He chose Atoq Navarro, who had studied the fabled gold and knew much about it. Navarro also led a team of highly trained mercenaries native to his homeland. With a large ocean tanker, countless weapons and vehicles, Roman was sure that these men would be proper for the job. He hired Navarro and his troops to aid in finding El Dorado as well as capturing Sully and Nate. Navarro was made to lead the mission. Unbeknownst to Roman, Navarro had his own agenda and was not planning on letting him have El Dorado. The mercenaries remained truly loyal to Navarro, only following Roman's orders as long as Navarro saw fit.
The mercenaries proved to be less useful than Roman had hoped, as Nate and his allies continued to defeat and escape the mass numbers of the mercenaries sent after them. They only hold back when Eddy's pirates are sent in instead.
It is unknown what happens to the mercenaries after Navarro's death, but it is probable they continued to be hired by other clients.