Please note that it is not official news. I saw many fansites guessed that the upcoming champion after Aatrox may be: Lucien, the Gun Templar. The evidences below shows that Lucien, the Gun Templar may be the new champion ZenonTheStoic works on.
In the last week or so, Riot's ZenonTheStoic has visited German side of the forums and dropped some hints about the upcoming champion.
"Yes I can confirm it won't take much longer, but i obviously can't give you a date.
The champ at the moment is actually "finished" from the creation perspective, but there are still two weird bugs (The ultimate scares me, at least theoretically, keeps showing to be very hard to use during gameplay tests. only when I use this champion I am twice as good as any other champion from that role, that shows that they're is kind of a "mastery" champion, also has a skill where you need to learn a lot before you unlock their full potential) Hmm what else can I let you guys know...during production I have tried about 5 different ultimates, that all were bad, and had three different passives, one of the old, removed, passives was so fascinating since it turned league as we know it upside down but just didn't fit the theme of the champion. Maybe we will use it in the future on another champion, who knows."
"Even if it is perhaps a little too dangerous as a teaser, here is one of my discarded Ultimates: you mark an enemy champion as a target (like Caitlyn's ultimate: a big target sign above the head). Then you shoot a missile that collides with the first enemy in any direction. After 1 second, the missile turns in the direction of the selected opponent. The missle has inertia and can only rotate a maximum of 15 degrees per 0.25 sec. Once it flies in a straight line towards the marked champion the missile accelerates, but cannot rotate anymore. Counterplay would be that the missile is no longer homing and "dumb fires", so you can step aside. So it was a homing missile that you could "throw" around Minion Waves or the enemy front line. I had extreme difficulties, making the ability sufficiently reliable for the player and at the same time fair to dodge for the enemy. I think it's possible, but the ability didn't fit in the Champion's kit in the end. (What the missile has done - damage, CC, marking for another skill - I leave open intentionally, :P)"
In short: In the 1st hint he is stating that the champ will be a bit harder to get used to
and will need practice compared to other champs being the same role. He also had
a passive for this guy, that turned the league as we know it around but didn't use it.
In 2nd one, he describes one of discarded ult for him as a curved bullet thing. The missile
can rotate around waves of minions to get better aim at enemy champ. This ult is discarded
keep that in mind.
I'm thinking that the champ is going to be using guns, looking at that discarded ult. I mean a missile can't be a sword or axe and it would fit bullet more perfectly. :P
So the leaked champion Lucien, the Gun Templar is what ZenonTheStoic working on?
PS: The images below is clickable for original size:
Also here is a video includes information about champion after Aatrox:
Reference: MMO Champion