Prior to the start of the Horus Heresy , Astelan rose to the esteemed rank of Chapter Commander of the I Legion and was stationed aboard the Dark Angels' flagship, the Spear of Truth. When the Emperor discovered Lion El'Jonson on the world of Caliban, the Space Marines of the I Legion celebrated. The Emperor informed them that the Dark Angels now had a new homeworld. This good news filled the Dark Angels with joy, for they were now far from their beloved Terra. The Dark Angels adopted Caliban as their own, and when El'Jonson was given command of the I Legion that had been created from his genome, the Terran-borne Space Marines of the Dark Angels thought it fitting. Astelan and his fellow Battle-Brothers thought it good that new Chapters of Dark Angels would be raised from Caliban’s people,