Kobus, ninth Count De Ruyter was a Redanian noble and commander who led the Tretogor forces in the Battle of Brenna. He was killed by a crossbow bolt, during a desperate charge against the Nilfgaardian "Venendal" division which prevented it from reorganizing in time to face the flanking attack of Blenheim Blenckert's forces. He was 56, at the time of his death.
He is also credited with writing "Strategy", a historical treatise on military manoeuvres.
In Act IV, Geralt first hears of the legendary "Raven's armour". In Act V, the witcher decides to reforge the armour from pieces of similar armour he finds. One of these pieces is said to have belonged to de Ruyter.
During Chapter II, Yarpen Zigrin mentions De Ruyter when reminiscing about the Battle of Brenna.