Yi (易) means "easiness", "change" or "divination" in Chinese.
Master Yi's name is a pun on the word "mastery".
"Wuju" is a reference to two of the developers at Riot Games. Namely, Andy Woo and Jeff Jew.
"Wuju", or "Wuji/Mukyoku" (無極 lit. Extremeless), is the grey field a taijitsu (the yin-yang symbol) is traditionally shown on, symbolizing "nothingness". It also nods to an old sword style honed for art in current times. In the Chinese servers, it is written as "Wuji/Mukyou" (无极), which means the same thing.
It bears similarity to "Wushu", the collective name of Chinese martial arts, mostly known as Kung-fu in western countries.
Master Yi was one of the champions chosen for the Ionian pool available during the Ionia vs. Noxus match. However, he was not one of the selected champions.
The goggles Master Yi wears (known as the Seven Lenses of Insight) seem to be an over-exaggeration of trifocal Night Vision goggles, and according to his background, provide a similar effect, allowing him to "see across a wider range of the spectrum".
His goggles can also be seen in the preview video for the Mac version of League of Legends.
In addition, his sword can also be seen in a later part of the video.
His costume and the goggles bring strong resemble to Sam Fisher from Splinter Cell game franchise.
A fan joke video give birth to a popular troll build called Dunkmaster Yi, focusing on going really fast, and the catchphrase "get dunked!".
Master Yi (sharing with Pantheon) is the Champion with the highest Base Movement Speed in the game, being 355.
Master Yi's sword resembles a katana, but is more of a dao (a curved Chinese blade that predates the katana's creation).
In terms of some of Yi's artworks (and his initial visual model) and his visual model update, he appears to be left-handed and/or ambidextrous.
Assassin Master Yi, Golden Alistar and White Mage Veigar are the only skins priced at 390 , making them the cheapest skins, excluding sale prices and free/promotional skins.
It was also initially in previous versions a mere black re-color of his default skin, though it can be implied that the dark tone of the skin is meant for covert blending, hence the name of the skin.
The new version of this skin instead features a more ninja-like theme, such as a face mask, a hoodie, and two kunai in the place of Yi's leg-wakizashi.
His normal skin along with his said Assassin skin has two spare wakizashi with one on each armored leg, though they have very little if not no use at all. His movement animations shows such a thing weighs down his running, but he may have adjusted to this via the skins without the armored legs.
Chosen Master Yi is a direct reference to the Jedi Knights of the Star Wars franchise.
After his visual upgrade in 2013, Chosen Master Yi's lightsaber causes a humming sound when attacking.
This skin's lightsaber changes colors based upon Wuju Style's current state: blue (normal), green (passive), red (active). This is similar to the Jedi Knight games which had blue, yellow, and red lightsaber stances; each altered the speed and power of attacks.
Ionia Master Yi is probably Master Yi's outfit while he is at his usual home, Ionia , or the outfit he wears in some special ocassions much like Blood Moon Akali or Blood Moon Shen.
His red color scheme bears resemblance to Sun Jian and the Kingdom of Wu from the Romance of the Three Kingdoms, in the Dynasty Warriors adaptions; the tree in the background also bears a slight nod to Jian Ye, the main captial of Wu (via its playable stage version in Dynasty Warriors 4/Shin Sangokumusou 3).
The skin's helmet and goggles also look very similar to the game Shinobi's main character Hotsuma, who would dash to his enemy similar to Master Yi's Alpha Strike.
In his Chinese artwork, there is the shadowy form of Cho'Gath behind him, who vaguely resembles the Aliens.
His sword is also more longer than the dao in his other skins, though with no effect on his auto attack range. The blade is also flipped to the other side in his idle stance in the inital versions of the game.
Master Yi's goggles were made and given to him by Heimerdinger.
Master Yi's entire kinfolk were killed with chemical inventions created by Singed.