Cornello was born as a half-Giant in the frozen North of the Shadowfel, in Vladimir's territory. Vladimir had a tendency to take mortal lovers for a time, and Cornello became one of these. However, by the time he reached his mid-40s, Vladimir realised that he was more attached to Cornello than the norm and did not wish to see him die of old age.
He did not want to create a new Vampire, having seen the results of Swayne turning Alyssa, but the only other way to grant Cornello immortality was either to wait for the Oluana Spring to be ready to discharge (which would take another 40 years) or to make him a lieutenant, and there were no pleasant lieutenancies on offer (he would have to be either skeletal or incorporeal). After much deliberation, Vladimir turned Cornello in secret.
When Rygax led a successful rebellion against Vladimir, Cornello was sent by his lover to hide in the frozen wastes where he would be safe. Afterward, Cornello returned and swiftly rebound the majority of Vladimir's spirits before they could be taken to safety, as the forces protecting them were only expecting attacks from the other Kings' territories, not from within.
These events must have happened after the Dead Wars, as the anti-VK bolts referred to Vladimir rather than Cornello. It is, after all, unlikely that the Ytarrans would not notice something so massive as the overthrow of one of the Kings.
As a half-Giant, he speaks Giant (fantasy-French). Although he has yet to be seen speaking common (fantasy-English), he clearly understood it when it was spoken by Voyvoda.