Amos Tillian was a Theelin male who specialized as a communications engineer. During the High Republic Era, he was employed by the Galactic Republic. Tillian, working alongside Kam, was part of Republic Communications Team Oh-Arr-Ee-Three-Six-One, which served as comms support for the Republic Pathfinder team led by Jedi Master Silandra Sho.
Tillian and Kam, his partner, came across a damaged EX droid. They successfully repaired it enough to determine that it was EX-8C, a droid that was part of Outer Rim Expedition Two-Five-Two. After they found a distress signal within the droid's stored data, Amos suggested that they should get in touch with the Pathfinder team they were collaborating with so that an investigation could be launched.
As they descended into Aubadas' atmosphere, Tillian was able to make contact with Obik Dennisol who was on the planet's surface, and they arranged to meet the team at their ship. Along with the others, he was guided by a native Katikoot to the ambassador's lounge found in Diurna, the capital city, where they waited for the Jedi to conclude their meeting with the Katikoot's leader. He was very impressed by the technology of the native inhabitants, specifically their hoversleds. The engineer enjoyed drinking a glass of Hibinacho juice; however, its high sugar content made him feel quite restless. Silandra Sho came back and told everyone else what she had learned from the Katikoot regarding the other Pathfinder activities. Tillian was reluctant to go to Gloam to investigate the missing team due to the potential dangers, so Sho asked him and Kam to examine the Katikoot's communications systems to try and understand the reason for the significant static and interference.
To examine the equipment, Tillian went to the systems hub located in the center of Diurna. He mentioned to Kam that he found it odd that local communication was being disrupted. Kam proposed to Tillian that they might be misunderstanding the problem, and that it might not be a failure of the equipment, but a deliberate act of sabotage. Excited, Tillian proceeded to the main communications relay to study the equipment and make a mental map of the circuit relays. He noticed an odd-looking power hub and asked GT-11 to remove it. As the astromech used its arm to pull off the casing, Tillian noticed it had a blinking circuit on it and realized it wasn't an actual power hub. Unfortunately, the discovery of the device led it to shutdown the entire system and terminate all the power in the city. He watched as Kam inspected the communications system. Tillian grew concerned that the Katikoot might imprison them for causing the city's power outage, but Kam reassured him. After Kam's attempt to fix the system briefly restored power before failing again, Tillian asked to take Kam's place to see if he could repair the system. He discarded the fake power hub and rerouted some of the system's connections. Standing back up, he instructed Kam to press a button on the console, which restored the city's power supply.
When the Pathfinders got back from Gloam, Tillian joined in the celebration of the conclusion of the Eiram and E'ronoh War.