League of Legends players believe they found a new champion to be released in January 2020. Last month, Riot Games announced in the champion roadmap that two new champions were being developed. A jugernaut, supposedly named Sett, and a marksman champion, which we now know as Aphelios.

Community Blog Surrender at 20  leaked new loot asset present in the 9.24 PBE Update, "Sett's Calling Card" is "Gained by impressing Sett. Openable on January 14th, 2020 at 11:00 a.m. PT." A potential tease during the League of Legends 10 Year Anniversary stream is also increasing the hopes of players that this may be in fact a new champion.

They suggest Sett can be seen on a TV in the background of Riot Game's office around the 25:58 mark. Seems like he will be a big guy:

Riot Games hints at the champion being connected to the ancient religious order Lunari, that worshipped the Aspect of the Moon. Based on the art depicted in the Champion Roadmap, it seems like the champion will belong in an arena, perhaps being a gladiator. 

Developer and lead champion producer Reav3 hinted at its abilities, saying it would thrive in the center of a brawl, and that the champion will be “laughing as they take hit after hit then furiously punching back, releasing all that stored aggression on their enemies’ faces.”  Sett is rapidly gaining a fanbase, with his own "Sett Mains" Reddit thread.