In development of Maokai, the model for his Sapling Toss was not completed before testing him out and was instead represented by miniature versions of the current champions' models walking around and blowing up on enemies.
Ryze, the champion, was named after Ryze, the screen-name of Riot Games' CEO Brandon Beck.
Tryndamere's name started out as the screen-name of Marc Merrill, Riot Games' president and chief marketing officer.
Ezreal was named after the screen-name of one of Riot's game designers, Colt Hallam.
Volibear was named after the Rioter Volibar, who led a faction on the forums fighting for the inclusion of an armored bear.
Zilean, who dislikes Volibear in game, was named after designer Zileas, who lead the anti armored bear faction.
Udyr also shares his name with a Riot employee.
It also means "beast" in Norwegian.
Banned in China: Similar to the issue with the Forsaken in World of Warcraft, Karthus was redesigned from a skull-faced lich to a withered, shadow-wrapped figure for the Chinese art, due to taboos about representations of skeletons in media. The only skins that keep their skull-faced appearances are his Grim Reaper skin (likely because it represents the more abstract personification of death) and his Pentakill skin (for reasons unknown).
Beam Me Up, Scotty!: Contrary to Memetic Mutation, Garen does not shout "DEMACIA!" when using Judgement (his signature Spin Attack). That's a separate skill, Courage, but seeing as how players like to use their defensive self-buff at the same time as getting up close to an enemy, the two are linked together in everyone's heads.
Defictionalization: Ever want to hear Pentakill's music? Now you can with their new album, Smite and Ignite, coming out on June 3rd, 2014.
A few days before Wukong's first preview blurb, competing game Heroes of Newerth announced its new champion: the Monkey King. Technically HoN created concept art first, but didn't do anything with it until rumours about a Monkey King in LoL surfaced. Needless to say, accusations of copying were flung from both ends despite the character clearly being a reference to Sun Wukong from Journey to the West.
All champions with more than 5 symbols in their names have shorter nicknames for typing. Usually just first letters of the name, but any short name that clearly identifies the champion in question will do. Veigar is sometimes called Vivi, Gangplank is Pirate, and Alistar is Cow.
Acronym nicknames are also common in order to shorten some character names for ease in writing on forums or chats. Gangplank is 'GP', Miss Fortune is 'MF', Jarvan IV is 'J4', LeBlanc is 'LB'. Master Yi seems to be an exception because he can simply be called 'Yi'.
Certain champs get their perceived overpoweredness reflected with a spin on their name. For example, Win Nao the Senechal of Demacia, Free Win the Blind Monk, Gankplank, and Feed-lesticks.
Second accounts are called "smurfs" (more or less officially, as Pendragon himself has one and calls it a smurf too).
This one extends outside of LoL.
The new Proving Grounds map has been affectionately nicknamed 'Murderbridge', due to the fact that its a bridge upon which lots of killing happens. Of course, it is also actually what the file for the map is called.
The Rated M for Manly champions Pantheon and Jarvan IV are affectionately nicknamed Mantheon and Jarman respectively.
Malzahar's Malefic Visions attack, due to the fact it spreads like a virus after killing the original target and because of the general spacey theme of the Void, itis often called "Space AIDS".
Most people know you're referring to Master Yi with the name "Samurai Fisher" due to his goggles having the similar glow effect.
Due to this "pro as heck guide to master yi", Master Yi is commonly nicknamed Dunkmaster Yi. Jarvan IV and Darius have also had the title Dunkmaster bestowed upon them by the fanbase as the animations for casting their ultimates resemble a one-handed and two-handed dunk respectively.
Vladimir's Sanguine Pool is an ability frequently used as an escape. Due to its ability to make Vladimir untargetable to things that are not already homing in on him while also speeding him, it gained infamy for its ability to completely save Vladimir at the last second or let Vladimir not help allies in need despite appearing to and was dubbed "Trollpool".
Fizz's Playful/Trickster abilities makes Sanguine Pool looks like it needs supplements when directly comparing escape abilities. Playful immediately makes Fizz hop on top of his trident to be invulnerable and untargetable to anything up to a very short duration and lets him cast Trickster which then has him jump away onto a nearby location - such as over walls. And place your allies back into impending doom, naturally. Needless to say, it did not take long for it to be known as the "Trollpole".
Kayle has been referred to as Samus, due to her similar design, similar Knight Templar attitude, and the fact that a limited edition skin exists that does nothing but take her helmet off.
Even during season 3 when Riot switched to a "3.x" naming convention for their updates, it still is common for patches to be named after the champion they introduce (Thresh patch, Lucian patch, Yasuo patch, etc.).
Aatrox and Thresh are often known as "Anthrax" and "Trash," respectively, among Dominion players due to them occupying the bottom-most tier within the Dominion metagame.
Garen is often referred as 'Bushren', since one of his 'common' tactic is to hide in the bush and then strike at any poor schmuck that dared approach his bush.
Mordekaiser is also associated with nicknames like 'Mordhuekaiser' or 'Hue(hue)kaiser' or any variations that inserts 'hue' on his name thanks to the Brazillian-related meme of "Mordekaiser es #1. HUEHUEHUEHUEHUEHUEHUE"
Fans of the lore generally believe that the first name of General du Couteau (Katarina and Cassiopeia's Disappeared Dad) is Markus.
One fan-held belief that is equal parts amusing and kind of disturbing is that, of the three yordle girls, only Poppy is Hidden Buxom under her armour. Kind of makes sense though when you consider that, as the only yordle of EITHER gender to be a melee-based bruiser (not counting Rumble, who rides a Mini-Mecha) she'd be a prime candidate for Boobs of Steel.
The original voice actress for Karma was Danielle McRae, who happened to be the voice actress of Painwheel. Unfortunately, when Riot decided to rework Karma in terms of gameplay and graphics, they replaced her with a different voice actress, but they kept Danielle's voice work of Karma for the "traditional" skin.
Ziggs and Rumble are voiced by none other than InvaderZIM and Raz.
Riot then released this "spotlight". Game Breaking... no, Game DESTROYING power, a "blurry" screen debuff, and the ability to kill members of your own team who defect to the other side. They released an actual spotlight video shortly after.
Their 2012 prank (a really bad 3D mode) was obvious (made even more so by the Urf cameo at the end), but nonetheless hilarious. Incidentally, they've actually named April Fool's Day "Urf Day."
Xypherous originally intended Nautilus to have an ultimate that involved picking up an enemy champion and spinning them around him. It, regrettably, simply did not pan out. He also wanted Nautilus to have a base movement speed even lower than the bottom-of-the-barrel 300 Nautilus has right now, but said they wouldn't let him make it any lower.
Wukong's kit was originally completely different, and stated to be very complex.
When Riot gave people a boost to get a Corki skin and reduced it in price...the people who missed it screamed so loudly they've since been very careful about that.
The developers don't often post in the forums because the average post is usually about as negative as the temperature in Antarctica.
Recently, a code to get a free skin for Caitlyn as well as the champion if you didn't already have her was put in the November issue of PC Gamer. A lot of people are reporting that people are going into stores and copying down codes printed in the magazine so they didn't have to pay for them. Several people have predicted that they won't be doing this anymore, even though PC Gameris combating this by having people email or call in with a proof of purchase to get another code.
More recently, when Annie's visual update was ready to be patched in, Riot announced that they'd release the Goth Annie skin for a limited time for players to buy who didn't purchase the Champion bundle it's normally exclusive to. This resulted in a massive outcry from players who valued the exclusivity of the skin, causing Riot to promptly retract the offer. Riot is now considering alternatives to such offers, but those who were looking forward to buying Goth Annie are going to have to keep waiting to complete their collections.