Chaplain Cassius is amoungst the oldest members of the Ultramarines Chapter.
Discounting those who fight on with the blessing of interment within Dreadnought armour.
Althoug close on four centries old, his ey remains sharp and his aim steady and his sturdy presence within the Ultramarines battle lines fills the hearts of his younger brethren with pride. Cassius can recal tales of the first Tyrannic war when he fought alongside Marneus Calgar, always "young Calgar" to Cassius, to purge Ultramar of the horrific denizens of Hivefleet Behemoth. His impassioned words have carried the Ultramarines forward into battle on a thousand worlds, firing them with his own deeply-held passion and belief.
When you use Chaplin Cassius in your army, he counts as an HQ choice.
Cassius is one of the few serviving veterans of the first Tyrannic war. He has fought in many battles against the Tyranids and understands them all too well. His hard won experience has led the Ultramarines to victory against these aliens, overcoming both their heinous weaponry and inhuman constitution. Cassius and any Ultramarines squad led by him may re-roll its dice to wound against Tyranids for any shots taken using rapid fire and/or pistol weapons. If the second roll still fails to wound, the dice may not be re-rolled again.
Any Ultramarines unit within 6" of Cassius may re-roll its Morale checks, accepting the second result as final. Note that this ability can be used even if a Morale check is passed on the first roll, so you can use it to try to make sure that the Ultramarines fall back in disadvantageous or outright dangerous situations (Cassius counsels with both strength and wisdom)
Unles accompanied by a bodyguard, Cassius is an independent character and follows all the special rules as detailed in the Warhammer 40.000 rulebook.
Cassius may be accompanied by a bodyguard as detailed for a Chaplain in the Codex Space Marine army list.