In a new Nexus post, Greg “Morgageddon” Lovasik went into detail about the work that went into making the Living Forge. It was a lot of work.
The original idea for him was to be a mobile shop, with lots of concepts being close to what we see now, but not quite there. This was in late 2013.
Ornn got put on hold once 2014 came around and champion reworks became a higher priority. In the end, the idea of having the forge embedded in his belly got passed on to Sion.
Years passed without Ornn being developed further, but he was revived in late 2016 as the team wanted to add a new top lane Vanguard to the roster. The timing for Ornn was just too perfect so the team could finish him up.
Ornn released on August 23, 2017 and has been a fan favorite in League. Players flip-flopped between thinking the champion was too weak and too strong, but we can definitely say he was worth the wait.