There's straw poll on Reddit asking what season people started playing, but all of the comments were of people stating what champ was released when they started. So, I figured I'd ask the boards too.
For me it's Lucian! In fact, the first log in screen I remember seeing is Spirit Guard Udyr. After that little event was over, it switched over to Aatrox for maybe a week until Lucian came out. :)
Vel'Koz was actually one of the many reasons why I started playing in the first place. I thought he looked badass in his Teaser: "First Contact".
i remember seeing rek'sai on the login screen and thinking "what the fuck is that?"
The earliest new champ I can remember 100%ly was Renekton. We were all freaking out about how OP it was that he can harass you under your own turret.
Hmmm...
The First Time i played was i think the last release was ~Khazix
When i came back with actual interest in the game it was Lucian
Wukong!!
Kha'Zix
Vi
Shortly before Kindred and Illaoi
Vel'Koz, I still see his release teaser as one of the best, the video is just perfect.
I started playing League shortly after it came out of beta, got to summoner level 9, forgot about it...
Found it again in preseason 3. Elise had just released, I think? I got placed in bronze in season 4 and haven't been able to play ranked since then, cuz I get banned so much
Not sure which one you'd count, so I just put both.
Fiora. In fact it's almost my anniversary because I started playing league after New Years around that time.
Ummm I think my first screen was Super Galaxy Rumble, but I remember seeing Braum's as well. I don't remember the order but one of those 2, I started playing around May.
Urgot. I joined somewhere around the time when he was in his first free week I think.
Braum.
I remember his release.
I think 
or 
... It was 2013 ;) ...
Either Jhin or Taric’s rework.
I am really not sure but I know for a fact, I started the game no later than Riven but could be as early as Orianna. Maybe a Rioter can tell me! this question is really on my mind. all the time.
Gnar, I started literally the day after his release.
I didn't start playing very actively though until around the time Kalista came out though.
and i dont mean her reworks but when her ult covered most of the lane 😂
but only by a couple of days because 
came out shortly after.
I joined the week Riven was released. I remember because all I had was Amumu, Leona, and Riven. And i waited a year or so then buying BB Riven as my first skin because i thought she was such a cool concept. Mow im here 5-6 years later still a filthy casual :^)
Jhin
I saw this guy on the login screen and thought it looked very strange, but very cool. Then I read his lore and got hooked immediately.
Ahri(I think), back when she was fun and less ridiculously safe and only had 2 dashes.
Pretty sure for me it was Wukong...
Swain or so
and 
...
The original Maokai and Karma. Back when League's lore was actually interesting.
Trundle, I think.
Lux
I'm pretty new :/
I'm really new so 
and 
Poppy.
Lulu. lol. I played before TRINKETS WERE EVEN A THING XD
I joined league around late August 2015 right when the juggernauts got reworked so I came in at a weird time and it was after 
Tahm Kench was released but a bit before 
Kindred got released. The login screen I remembered was the arcade one.
BTW, do you have the link to the reddit straw poll?
For me it was Udyr, released on 12/02/2009...yeah, I've been around for some time Before that Shaco and Heimerdinger were released*[zombie-brand-mindblown]*
Kled. he was released like 2 weeks after I started playing.
Between and
Fiora [fiora-cool]
I remember seeing 
on the log in screen when I first started.
I thought she was kind of a mascot for the game until the next champion came out and it changed lol.
