An Illyrian science vessel encountered in the Delphic Expanse in 2154, from which a desperate Archer steals a warp coil, leaving its innocent crew years from home.
The Illyrian ship appears in the Enterprise episode Damage. After the Xindi attack at Azati Prime, Enterprise is barely holding together and cannot go to warp, yet Archer has only days to reach a meeting with Degra that may stop the weapon being launched against Earth.
Enterprise answers a call from an Illyrian ship that has itself been damaged by the Expanse's anomalies. Its captain is friendly and willing to trade, but he will not give up his warp coil, because without it the journey home would take three years.
Archer, to T'Pol's dismay, leads an armed boarding party and takes the coil by force, leaving trellium-D and supplies in exchange. The raid is treated as the moral low point of the mission. The Illyrians themselves became more prominent later in Strange New Worlds.