At the onset of the 13th Black Crusade, his regiment was posted to the Forge world Hydra Cordatus. The Jouran 383rd were tasked, along with elements of the Imperial Fists Space Marine chapter, with defending the stocks of gene seed held on Hydra Cordatus from a large invasion force of Iron Warriors Chaos Space Marines.
The Imperial forces managed to hold out for many months until they were finally overrun. Lietuenant-Colonel Leonid was tasked with destroying the stocks of gene seed, but there was too much gene seed and not enough time, and Mikail and his men were captured along with the remaining gene seed. The Colonel, along with his regiment, were presumed missing in action and their names were entered into their regiment's annals.
Leonid and the surviving Jouran Dragoons were taken into the Eye of Terror to work as slaves on the Iron Warriors' adopted planet of Medrengard. After years of slaving in the forges of Mendengrad, Leonid, along with his colour sergeant Gavin Ellard, were rescued by a band of renegade Space Marines, led by Ardaric Vaanes. Later on, led by Captain Uriel Ventris (formerly of the Ultramarines chapter), they managed to help destroy the remaining gene seed stolen by the Iron Warriors. However, during the mission, Ellard succumbed to wounds caused during the escape from the fortress, even after surviving an encounter with the grotesque Savage Morticians. Colonel Leonid sought to avenge his long-time friend by aiding in the destruction of Warsmith Honsou's fortress, Khalan-Ghol. He died by his own hands, sacrificing himself and the last member of his regiment by detonating a melta bomb, also killing a horde of daemonic beasts known as the Sarcomata in the process.
- 1: Storm of Iron (Novel) by Graham McNeill, [Needs Citation]
- 2: The Enemy of My Enemy (Short Story) by Graham McNeill
- 3: Dead Sky, Black Sun (Novel) by Graham McNeill, [Needs Citation]