John Quoteman
Who's that faction?
HERESY!!!
Big Dakka
Mystery Box!
100

They are my Space Marines and they shall know no fear.

The Emperor of Mankind (Big E)

100

In a galaxy built on war crimes, they are the most debased war crimers of all time.

Dark Eldar (Drukhari)

100

Skulls for the skull throne!

Khorne

100

The basic weapon of an imperial guardsman

Lasgun
100

Space Vikings

Space Wolves

200

You forget one thing brother, it is also a hammer.

Vulkan

200

The boys, the lads, the _

Da Orks, WAAAAAAAAAAAAAAAAGH!

200

The arch traitor himself

Horus Lupercal

200
The standard rifle of a space marine (this has many variants but looking for the base weapon).

Bolter

200

Homeworld of the Salamanders

Nocturne

300

The time for speeches is done, The first great test is here. My order to you all is simple, yet heed it well, and exert yourselves to see it done.

They are coming. Kill them all.

Rogal Dorn
300

A clone based society of hyper space capitalists who highly value contracts (and were totally wiped out at one point but ignore that retcon).

The squats/Leagues of Votann

300

This traitor legion is devoted to Tzeentch, the changer of ways.

Thousand Sons

300

What Orks call their guns

Shootas

300

What's the fastest color? (to orks)

Red uns go fastaaa!

400

Death is nothing compared to vindication

Konrad Curze

400

The oldest race/faction in the galaxy that is also the most technologically advanced

The Necrons

400

The most zealous chaos worshipper legion who's primarch only ever wanted the truth. Ironically his book on worshipping the Emperor is the basis for the modern Imperial Cult. (I'll take the legion name or their primarch as an answer).

The Word Bearers/Lorgar Aurelian

400

This weapon breaks its targets down to the atomic level, most commonly seen being wielded by Necron Warriors.

Gauss rifle/flayer

400

Who is the current leader of the Black Legion, herald of the Black Crusades who seeks to finish what Horus started?

Abbadon the Despoiler

500

Courage is fighting the kingdom which enslaves you, no matter that their armies outnumber yours by ten-thousand to one. You know nothing of courage. Honour is resisting a tyrant when all others suckle and grow fat on the hypocrisy he feeds them. You know nothing of honour.

Angron

500

A force that (seemingly) has the galaxy entirely surrounded, draining worlds dry before moving on to the next.

Tyranids.

500

The name of the greater daemon of Nurgle.

Great Unclean One.

500

An anti vehicle weapon employed by the Eldar

Brightlance

500

What was the name of the apocalyptic war between the Necrontyr (eventually Necrons), and the C'tan vs the Old ones, Eldar, and Krork?

The War in heaven