IRW Solius was a Romulan starship, a D'deridex-class warbird battlecruiser in Romulan Star Empire service in the early 25th century. In the 2400s decade, the vessel was part of the Tal Shiar. (STO - Empire mission: "Friend or Foe")
In 2409, the Tal Shiar received personnel and material from a Great House of the Klingon Empire. Research was relayed through the Yridian-operated Klingon space station Logner Beta 3 in the Vor system.
Early in that year, Commander Chavek and his warbird received a distress call from station commander Plardos Yardin and traveled to Vor II. Chavek confronted a Klingon Defense Force vessel carrying Ambassador K'mtar investigating the House of Torg. Chavek's warbird was destroyed in the ensuing confrontation. The Solius and its escorts set course to Vor II.
The Tal Shiar's activities had been tracked by RRF Commander Telek and his crew. They had not been powerful enough to engage Chavek directly but fought alongside K'mtar's ship when the IRW Solius arrived with Tal Shiar reinforcements. (STO - Empire mission: "Friend or Foe")