Stephen Bliss has shared some insight into how he was hired by Rockstar Games.

Bliss was cover artist for Rockstar from 2001 to 2016. So, all the cover art for Grand Theft Auto, from GTA III all the way to GTA V, was produced by him.
Bliss also made art for other Rockstar games like Bully and Red Dead Redemption, as well as additional art, such as loading screens or promotional illustrations.
In a video on Twitter, Bliss revealed that Rockstar took an interest in his artstyle after seeing his design work for his 1998 apparel brand, Steroid.
He then shared a few pictures of some of the shirts and designs he made for Steroid, and even some for Rockstar itself.
As it turned out, Rockstar Games were interested in making their own lifestyle brand. So yes, if Rockstar was not the first game company to make apparel, they were definitely one of the first to be successful at it.
You can learn more about it in Stephen Bliss’ video below.
