The first thing that came to a lot of peoples mind, myself included, when the Champion known as Tahm Kench, regarding his abilities and ingame playstyle, got revealed was probably:
"Dafuq is dat thing? Why...why is he eating everything and...what..."
A major part of what we know about Tahm Kenches Background is the story of a gambling man in desperate times, the Cinematic named after the champion who is teasered: The River King. Narrated by Tahm Kench himself, it is the tale of the odyssey of The Gambler who lost all he had to his gambling and was about to give up on his occupation just before he got offered a bargain from The River King, eventually starting a new life, still gambling, with the beasts part of the deal beeing to satisfy his hunger when the time is right. The Gambler married his wife but soon after lost his riches, his property and eventually even his wife to The River King as everything got feasted upon. The Story ends with The River King departing, leaving the ruined Gambler to his end which is left open.
Now that probably didn't help understanding this guy. Not on the first look. So let us start with the main thematic aspect of this champion: Eating. His unique Nutrition is seen at The River King's Ending just like ingame: The huge beast, which is cutting deals to satisfy its appearently huge Hunger, is feeding itself with a few mere Goldcoins and Wedding Gifts before entirely devouring a complete House while still not beeing filled to the brim after that meal. At this point everyone, no matter how slow one can be in terms of catching up obvious stuff, should understand that T.Ks Hunger can't be a normal Hunger. To top things of, he then eats the Gamblers true love, his wife, and departs due to beeing satisfied entirely.
And another question was troubling a big bunch of people: If he's such a big dude, undefeatable, why isn't he just "crashing any party whenever he wants?". If he is really so hungry, why is he waiting multiple years after his unneccesary deals with people and is not just devouring them instantly? He has an aquired Taste but what does that really mean?
The answer is: He does not hunger for food. He hungers for despair and sadness, which is also mentioned in his Lore. He does not use his big mouth to eat the stuff he wants to eat, but rather create misery with it which he can then feed upon. In the Story of The Gambler, he used to eat all that was important to him, leaving him forlorn. As T.K. is a man of age, he of course wants the maximum amount of despair possible for his meal: The lack of Gold leaves the Gambler bankrupt, the Gifts taken from him let him regret his deeds, him losing his House makes him worry about his family and his own life. But with the loss of his Wife, the women he used to love, his life seems useless, ruining the man forever. As this happens T.K. is able to sate his unusual hunger and disappearing. But how and, more importantly, where is he heading?
His Quote: "All the world's a River, and I'm its king. Ain't no place I ain't been; Ain't no place I can't go again." has become his most remarkable phrase since it seems so important that it even made its way into his Ultimates Tooltip. The major profit about dealing with Tahm Kench is that he is able to take you to appearantly everywhere, since he can travel there through whirlpools. While the whirlpools are not specifically explained, the ability itself is. He is confirmed to be something special, not just a creature with a strange diet, but a Demon, the kind of "Satan-in-a-tuxedo"-Demon offering Deals-with-the-Devil to claim souls or something. As it was pretty easy to understand the fact that he feeds of despair, how exactly he gets people to special places through Space and even Time remains shrouded.
And this is the part where his Lore in terms of Runeterra gets important, his real identity and the actual deal with and through hunger.
Even with all this information, there are still a few questions open in the Fable of The River King: Where did The River King come from, why did he chose The Gambler in peticular and what is Tahm Kench talking about when it comes to the Hunger of The River King and The Gambler? Believe me or not, the Hunger is the way The Gambler travels and how he loses all his aclaim in the story. And this has to be explained.
The Gamblers only Hunger is Dice and Cards , so his addiction to gambling all in all. As he was about to stop this and start a new life all over again The River King intervened, tempting The Gambler to take his old habbit with him as it is his Hunger, his Devotion. He already knows the price at that point: He will most likely lose everything again because of the financial pressure but he does it anyways. He takes the deal, he lets The River King in. Eventually, The Gambler could have gone anywhere after leaving Bilgewater, but The River King takes him to a Palace of Chance. While there is no additional information about this place, if it is a known place in Runeterra or The Gamblers new Home, it is incredible unimportant at the same time. It is just the place his Hunger has driven him to, the destination The Gambler would have liked the most. This way, Tahm Kench transports people, since a lot of people seem to not understand how he can travel anywhere through a River of some sort and how he was and could be anywhere. The River is basicly just the World/Existance itself, going on and on.
And all this is basicly wrapped up in his appearance: A catfish-frog-thingy, wearing two old sewn-together coats, some rings and an aged Top Hat, plus his remarkable whiskers-mustache. The attire, trading attitude and language of a gentleman while his accent, his rugged quality of clothing and gluttony is more southern and hillybilly-ish. A clear contrast between the seducing and beneficial Profit The Gambler could make by taking his gambling habbit with him through "fairly dealing" with The River King (implied by the nobly attire, accessories, fine language etc.) and his intuition of him getting scamed (and metaphoricly "eaten") by a Demon (implied by his identity as a huge, hungry monster, southern accent, tattered clothings). The Gambler is taking a Deal while he already knows that he is going to be ripped off, after all the monsterous hungy beast in a coat talking fancy words is still a monsterous hungry beast, right? That is the reason he is considered a Fool in the fable, as he is doing something unreasoned just because of his hunger. He loses everything he got after all even though he could have prevented that. How he lost everything, well, that's up next.
With a slight foreboding of questioning the existance of somebody "offering a deal" who "sang a song" and everything, how exactly does The Gambler lose everything at the end of his journey? As he is making a pact with himself and as there is nobody he met at a River after all, there has to be someone who devoured all of his aclaim. The Gambling Addiction, his only Hunger did cost The Gambler everything he had: He spent all of his money to gamble, he sold or had to give away all the wedding presents, he even lost his house because of his doubts. Because he had overdone it on his Hunger he was now losing everything to his Hunger just as he had foreseen it in the appearance of The River King. Eventually, he even lost his wife in the process (maybe she left him, maybe she got kidnapped and/or murdered by the mafia or something....) which left him ruined and made the evil spirit leave him which was all about entering him because of his desires and ruining him over time. This is also what Tahm Kench meant by beeing "let in".
Concluding, The Gambler never "dealt" with anyone but himself as he started his new life. He took the Hunger for gambling with him even though he knew it would ruin him again. In the end, it plainly ruins him just as promised and probably marks his end. All is let by a spirit titled "The River King".
"Titled" might be a strange word right here, as we are coming to the end of the interpretation of The River King and the motives of the Champion known as Tahm Kench. Who exactly "named" him, how do we know about this story? The Story is a fairy tale, told around Bilgewater, a trading city where greed, envy and gluttony are all around. The story is told by the Elders of Bilgewater to remind the younger generations to not blindly follow your deepest desires as the Monster called "The River King" will show interest in you, luring you into feeding it with all your aclaim. This story is probably really old and has been told in a million different versions before, as the meaning is very flexible to tell (you can probably think of one yourself, it's just someone losing everything to his greed...). The current version and the naming of the Spirit known as "The River King" is based of a story that most likely really happend: The Gambler that lost everything in Bilgewater to his Greed. The Spirit is shown as a representaion of the Gamblers dark Urges and is most likely a catfish in a River because that's what's imaginable around Bilgewater (remeber this is a fairy tale, the Spirit could be looking entirly different in other cultures like Freljord for instance). In the Video of The River King, throughout the entire Cinematic, all you see are pages drifting around in a River near Bilgewater, probably the pages of a Fairy Tales Book, right? There are illustrations on every page about what is happening, there are only a few letters/sentences on every page, easily readable even for very young folks.
As it is probably getting harder and harder to read these long drawn out sentences, I just want to clarify one thing that blew my mind once I found out: There is no evidence for what happened to The Gambler after he lost everything. One of the coolest things in my opinion about the entire cinematic is the Humming of the Spirit as The Gambler is getting lured. As this melody even made it into T.Ks ingame emotes I was really looking forward to the Login Screen , just for me to discover the familiar tune beeing hummed by someone else than The River King. At first I did not quite understand who it was that sung this song of desperation and regret, but I imagined the last moments of The Gambler something like this:
After The Gambler lost everything he went to the nearby River which he followed to get to the palace of chance, sat down at the shore and thought about everything, desperate, ruined, crying about his loss and his failure of a new beginning as he remembered the song he heard as he was about to leave Bilgewater. He stared at the water, humming the song of The River King, his decision already made. Eventually, his song found a quick end as he leaped into the waters, explaining why the distinctive tune only stays through the first half of the Song . In his life some called him a King, some called him a Demon, in the end the Water of the endless River would forget the Names of the Drowned. But not his Name though, as the tale is told to the current date in Bilgewater.
The Name of The River King changed over the years but the current version of the story gives him the Name of the man who got consumed by his own Hunger and Greed. The Gamblers Name was Tahm Kench.