Sirae Karagon
Sirae Karagon is the Red Scorpions Ancient-Invigilus: guardian of purity and bearer of the Vexilla Imperialis, the standard that the High Lords of Terra awarded to the Scorpions for their successful pursuit of the Badab campaign against Lugft Huron. Due to its impressive pedigree, the banner immediately became one of the Chapter's most precious relics. It acts as a galvanising force for the Red Scorpions, making them fight on even in the direst of circumstances.
The standard itself was given to Karagon by Carab Culln for the badass feat of defeating a Genestealer Patriarch, then throwing it from the peak of it's hive city spire-top lair. Karagon was raised to his position of Ancient-Invigilus when Culln fell against the Tyranids, a rank that gives him the authority to scrutinise the commands of the Lord-Regent, but is also meant to hold his confidence and ensure he retains his humility in his position of power.
On the Tabletop
Despite his amazing model, Forge World tells us to use it as a regular Chapter Ancient. He was supposed to get rules in Fires of Cyraxus, but we don't know if that book is ever coming out.