"Lo, in the histories of the many Chapters of the Adeptus Astartes, every Primarch listed that has ever come across my sage and learned eyes, has found root and home upon a planet, which hath shaped and set in stone the character of that warrior of The Emperor that he would become.
Therefore, one must give pause to the Primarch of our brothers, the Angry Marines, that great warrior of rage for he hath never fell upon a planet. Nay! Legend has it he was borne upon the ethers and drifts of space, alone in his capsule save for a discarded copy of Battletoads that The Emperor had thrown out, a legendary artifact that hath fueled research into vast weapons of war that it might be unmade and erased from history.
When the capsule had finally been rammed into a drifting hulk of an old Imperial battleship, it is said that the Primarch was so enraged and frustrated with the vile game that he headbutted out the Adam's apple of the first survivor that he encountered, and thereafter killed every inhabitant with the remnants of the dying initial combatant."

--- Historian Nwabudike
Histories of the Ill-favored Chapters