Graham McNeill

A writer for the Black Library.

Not Dan Abnett, but forms the Holy Trinity of Black Library writers with him and Sandy Mitchell, (Which makes ADB the holy child or something)

Wrote the Ultramarines novels and some Iron Warriors shit. When he's writing them, the Ultramarines are not just tolerable but actually awesome.

He's also written several Horus Heresy books, including the infamous short story The Last Church.