There is no greater bulwark than the Praetors of the Adeptus Custodes, the bodyguards of the Emperor of Mankind.

Vexilus Praetor

Flash
Vigilance
Aegis of the Emperor — Commanders you control have protection from everything.

Warhammer 40,000 Commander

Protection from everything means that commanders you control can't be the target of any spells or abilities, they can't be blocked, nothing can be attached to them, and all damage that would be dealt to them is prevented. They can still be affected in other ways (such as by Their Name is Death, for example).