Alpharius

The last of the Emperor's primarchs to be reunited with his father and his Legion, Alpharius remained the most enigmatic of all the twenty, a figure so shrouded in deliberate obscurity that even his fellow primarchs struggled to take his measure. He rebuilt the XX Legion in the image of his own subtle genius, teaching them that a war won through guile cost far less than a war won through slaughter, and that the greatest victories were those the enemy never understood he had lost. Under his hand the Alpha Legion became the Imperium's masters of espionage, infiltration, and the long, patient stratagem.

Alpharius guarded a secret that reached to the very heart of his Legion: that he shared his identity and his command with a near-identical twin, Omegon, the two brothers presenting a single face to the galaxy. When the Heresy came, Alpharius led the XX to Horus's side, yet whether this was true treachery or the outermost layer of a deeper design remained known only to himself and his twin. He fought the civil war as he fought everything, from behind a veil of misdirection, and the ambiguity of his true purpose endured long after the war itself, an unanswered question wrapped around a primarch who had made unknowability his masterwork.