Renekton was first revealed in the Journal of Justice, Volume 1 Issue 8, as the brother of Nasus, though his name was spelled Renekhton there. It should be noted however that Renekton has technically been in the lore as long as Nasus has, as the story of the conflict between the two brothers has been in Nasus's backstory from the start.
His title was previously The Eater of Souls, but was changed to the current title by Riot after his sneak peek.
Cull the MeekCull the Meek was originally called Tyrant’s Reach but was changed with the release of the Champion Spotlight for unknown reasons.
Renekton's Art Spotlight is the only one that is not of his original skin, but his Outback skin.
Renekton and Nasus both bear resemblance to old Egyptian Gods, namely Sobek and Anubis. However, Renekton's lore is more resemblant of Ammit, a half-crocodile demon that, upon Anubis's judgment of a heart being impure, would eat the heart of the impure one. This is similar to Renekton's judgment of who was worthy of receiving Nasus' teachings.
In his lore, it states that he awakens in the sewers of Zaun. This is a reference to the urban legend that crocodiles live in the sewers of various large cities.
Renekton's blade-weapon may be a reference to the Klingon bat'leth, from the Star Trek series. Although, Renekton's blade has the grips on the inside edge of the blade where as a traditional bat'leth has them on the outside edge of the blade.
In the polish version, Renekton's /joke and /taunt are both quotes from a YouTube video that's popular in Poland. It is worth noting, however, that curse words are substituted with their less offensive counterparts.