Josh Reynolds
An author of Black Library who has worked to fill the plotholes of Warhammer Fantasy and develop the Age of Sigmar setting.
He was put in charge of writting the first and fifth novels of The Endtimes (The Return of Nagash and the Lord of the End Times), doing his best to actually bring a decent narrative to what is arguably Games Workshop most controversial action.
After that he has been in charge of fleshing out the Age of Sigmar universe, which has allowed the development of the Stormcast Eternals in quite interesting characters (he brought some female stormcast and worked to bring some character to Tornus The Redeemed), he is also developing a cast of characters for his stories, allowing for AoS to have its own dramatis personae.
Additionally expanded the fluff for 40k, expanding characters such as Fabius Bile and Trayzn the Infinite.