You are human. That is the whole of it. The Inquisition of the Imperium does not recruit from the xenos, the mutant, or the abhuman — and neither does this game. The only playable ancestry is Human. Your character's Ancestry line records it plainly, because a line that needs no argument is the most honest kind.
That is not to say the galaxy holds only your kind. Xenos, mutants, and the twisted children of the Warp walk every world of the sector. They are simply not played. You meet them — as allies to watch, rivals to endure, and enemies to purge. When you build a character, you build a subject of the Throne: flawed, faithful, and expendable in exactly the measure the Inquisition requires.
Your place in the Inquisition
You are the newly-minted Inquisitor, heir to the warrant and the duties of your late mentor, Inquisitor Kane. Around you stand the people of your retinue: the veterans, adepts, and specialists who make an Inquisitor's word into action. The classes in the compendium — Soldier, Tech-Adept, Sister of Battle, Sanctioned Psyker — are the roles such a household takes on. Whatever your class, the oath is the same: Innocence proves nothing.
The rest of the sheet
Your attributes and skills shape every roll you make — see Attributes & Skills for how they work. Your wounds, talents, proficiencies, and inventory fill in from there. But none of it changes the first fact: you are human, and that is enough to be judged by the Inquisition, and enough to be saved by it.