Jax and Darkin Involvement Theory
So I just got done watch Redmercy's video about Jax and stuff and one thing i just now noticed about the splash art with Aatrox in it is... Aatrox isn't behind Jax, he's in the fire of the lamppost.
http://i.imgur.com/N7eKMlB.jpg
Take a look. See how the figure ends and begins at the flames of the lamppost.
Jax's title Grandmaster at Arms is that because he's so talented with weapons but what if those weapons were possessed to give his great power. That figure wouldn't have to be Aatrox but any Darkin who could put his energy into any weapon. This could be why Jax handled his limitations so easily when they were forced upon him. He was outlawed from using weapons so he just ripped a lamppost out of the ground an d decided to use it, probably because the Darkin would transfer it's power into the make shift weapon.
Another reason why Jax could not want to switch his weapon is because it could actually allow him to use even more power.
I.E. His empower ability could just be the strength of the Darkin in it's purest form. Releasing the Darkin because as shown in A New Dawn Jax has to break the Lamppost to even use Empower.
http://soocurious.com/fr/wp-content/uploads/2014/07/jax.jpg
http://th00.deviantart.net/fs71/PRE/f/2014/203/7/d/a_new_dawn_wallpaper_11_by_tomok2404-d7rrqgl.jpg
Jax's Species
When I first started playing League I just assumed that Jax and Yi were of the same race, then I found out Yi was a human with a modified helmet.
After looking at Trundle a bit, as far it looks like Jax actually might just be a very clean troll. The amount of eyes he has is obviously a mask because in different skins which have a little bit of canonical appeal on them he has different patterns on them. Look,
http://static.mnium.org/images/contenu/actus/LOL/jax/lol_jax_classique_splash_hd.jpg
http://ddragon.leagueoflegends.com/cdn/img/champion/splash/Jax_6.jpg
http://ddragon.leagueoflegends.com/cdn/img/champion/splash/Jax_2.jpg
Now back to him being a troll. Let's get a fresh look at Trundle, a "Wild Troll" and Jax to compare the two.
http://41.media.tumblr.com/9090a1807a3f432934fdb65a6c3b9164/tumblr_mvejmeHZ571rfyiu4o1_1280.jpg
http://static.mnium.org/images/contenu/actus/LOL/jax/lol_jax_classique_splash_hd.jpg
They both seem to have cold colored skin, they both have three fingers, they both have pretty wild teeth and finally they are both stocky people. I t really isn't much of a stretch since when you look at a clean image of Trundle without the rock on his skin he seems like he could easily form into a society.
http://fc05.deviantart.net/fs71/i/2014/062/1/8/trundle_by_milkydayy-d78qyf1.png
Save that beard down and put on some good clothes and BAAM, you've got a civilized troll. If Jax isn't a troll then he'd probably be one of hte ancient people that Aatrox defended thousands of years ago who's survived because of reasons.
TL DR/Rap up
My theory is that Jax isn't a Darkin but his Lamppost has the power of the Darkins for any reasons from Jax stealing it to him having the grace of a Darkin. Whatever he is Jax bears uncanny resemblance to Trundle a troll and might be one himself just fully clothed. If he isn't a troll he's either an ancient or something that has yet been revealed to us.
Edit: I just another realized thing. Jax's judgement as a swift one, the fastest in league history. A judgement is the assessment of the persons wind, reading their sins to know who they truly are (basically) If Jax is a troll who are known to be a very straight foreword and clear agenda based people this would only increase his chances of being a Troll since if he was an ancient he'd clearly have a goal that would take a long period of time to go throughout and understand.
Not many humanoid races are as straight forward as trolls, unless there is something else out that unlabeled.
Edit #2:
Could you bring up the resemblance between him and yi's goggles, perhaps they have some relation too.
Sure no problem.
http://ddragon.leagueoflegends.com/cdn/img/champion/splash/MasterYi_0.jpg
http://ddragon.leagueoflegends.com/cdn/img/champion/splash/Jax_0.jpg
http://static.giantbomb.com/uploads/original/8/89672/2119146-jax_templeskin.jpg
When I was first skimming throught the champions and thier lore about a year and a-half ago I just assumed that they were the same race of probably techno warriors or something but I later found out that Yi's helmet was made by The Donger aka Heimerdinger. jax face clearly is a mask atleast a face mask not a full head covering mask like the Mando'a.
Sort of like Robins, or other old timey Comic Book Super Heros.
ex.
https://s-media-cache-ak0.pinimg.com/736x/40/e9/7e/40e97e558773d323f716acbdaeafa03e.jpg