RICK! RICK, The place is gonna blow! PUT ALICE ON!
~ Wade telling them that the Stacks are about to explode
Innovative Online Industries, abbreviated as IOI, is the main antagonist faction of the 2011 science fiction novel Ready Player One by Ernest Cline, and its 2018 film adaptation of the same name directed by Steven Spielberg.
They are an Internet service provider and communications conglomerate seeking to gain control of the OASIS by exploiting a loophole in James Halliday's "Easter egg" hunt to determine the next owner of it.
Prior to the "Easter egg" hunt, IOI was a company that sold services within the OASIS among other things. Presumably founded after the OASIS launched, IOI gained a reputation as the world's largest internet service provider by acquiring (or forming) hundreds of telecom companies, big or small. After James Halliday died and left ownership of the OASIS up to whoever could complete his "Easter egg" hunt (finding three keys and delivering them to the correct location) IOI decided to exploit a loophole in the hunt by having one of their employees complete the hunt which, through a legal contract, would ultimately cause ownership of the OASIS to fall to them.
To do this, IOI assembled a team of Halliday and 80s pop culture experts to complete the riddle Halliday had left behind alluding to the first key's location, as well as an in-game army of their employees to recover the key and complete the quest, headed by their Chief Operations Officer (CEO in the movie) Nolan Sorrento. Their army was dubbed the "Sixers" due to each of their usernames being their IOI employee ID, which always started off with a "6".
However, the first person to find the Copper Key was not an employee of theirs, but a player by the username of "Parz3val" (real name Wade Watts). IOI instantly set to tracking him down to cut a deal with him and get him to turn over the key but Wade refused, prompting them to go with their backup plan of blowing up Wade's trailer in an attempt to kill him. However, Wade survived the assassination attempt, not being in his trailer at the time, with IOI managing to only off Wade's aunt and her boyfriend.
Despite this, IOI eventually managed to obtain all of the keys and track down the location for them to be inserted, a castle on Planet Doom. They faced opposition from an army comprised of a large percentage of the OASIS' users, resulting in a showdown between IOI and the OASIS players while Parz3val and the other members of the "High Five" attempted to make it to the keyhole before IOI could complete the final puzzle. Only Parz3val managed to make it there, though he still succeeded in completing it before Sorrento or any of his Sixers could, resulting in ownership going to him rather than IOI.
It is unknown what happens to IOI after this, but it can be safe to assume that the company was shut down, after being accused of blackmail, terrorism, murder, and attempted murder (at least for Wade, Art3mis, and Shoto), and the board of directors arrested and tried.
In the film, IOI plays a relatively more smaller role. In the film, IOI is a video-gaming corporation that makes the virtual reality equipment (they control people's access to the OASIS). Unlike in the book, IOI is never shut down, but restructured as a business by Wade and the High-Five.