Macias was a citizen of Juhraya, a Federation colony that came under Cardassian rule after a treaty was signed with the Federation. He was the leader of a Maquis cell that opposed the treaty.
After Juhraya found itself in Cardassian territory, Macias was dragged from his bed and beaten. The authorities did nothing other than to agree with him that it was an unfortunate situation. Soon after, he left his colony and joined the Maquis.
Lieutenant Ro Laren was sent by Captain Jean-Luc Picard to infiltrate his cell in 2370 after returning from two years of training in Starfleet Tactical. Ro sympathized with Macias and the Maquis for their struggles and the two became very close in a short space of time. Macias was fond of particularly spicy hasperat, after being introduced to it by a Bajoran friend who was later killed during the Occupation of Bajor. Macias reminded Ro very much of her own father, who was also killed during the Occupation when she was just a child.
Macias' cell was ambushed by a group of Cardassians posing as Bajoran monks and Macias was killed in the ensuing firefight. Following his death, Ro joined the Maquis. (TNG: "Preemptive Strike")
Macias was played by John Franklyn-Robbins. According to the Star Trek: The Next Generation Companion, 2nd ed., p. 297, the character was named after a Cuban freedom fighter in Cuba's War of Independence from Spain.
The character was Bajoran in an early draft of the script.
His name was spelled "Macius" in the Star Trek Customizable Card Game. In the comic Star Trek, Issue 12 (2022), a a text titled Macias Kodan, The Collected Works is described as containing the true history of the Maquis.