Who is he?
He is the leader of a race of echindas that was supposedly extinct. Everyone in Sonic's world only them as 'The Fourth Great Civilization' when in reality his clan is one that rivaled Knuckles' clan, the Pachacamac. Imperator Ix' clan is known as the Nocturnus. He is a power-mad ruler who is bent on ruling the outside world of which he was taken from. After he was taken, he arrived in a nightmare dimension known to its inhabitants as the Twilight Cage which consists of little planetoids.
He is shown as a bit war-hungry. He is war-hungry because he wars with the inhabitants of the Twilight cage as soon as he arrives. He is also incredibly stubborn, not willing to surrender under any circumstances.
The planetoid inhabitants
There are six planetoids in the Twilight Cage total. There a total of five different races living in these planetoids. They are: the Kron who are rock-like in appearence, The N'rrgal, who appear to look like giant transparent slugs, the Zoah who are a war-like race, the Voxai who look like floating manta rays who happen to have two planetoids, and then the Nocturnus who are the most recent additon to the Twilight Cage which is basically another clan of echindas.
Ix is very interested in the Chaos Emeralds, so much so that he sends some of his echinda soldiers to Sonic's world to steal them. Right now Sonic and the gang don't know that these are more echindas but that they are a group of theives who they call The Marauders, the leader of whom is an echinda named "Procurator" Shade. This is also not know by our heroes until later events in the story cause Shade to reveal her identity.
Ix's soldiers had succeded in taking all seven of the Chaos Emeralds with no problem. The game stars out as a search for Knuckles who had been kidnapped by the Marauders. After Sonic and friends rescue Knuckles, they make a horrible discovery: Angel Island, the resting place of the Master Emerald of which Knuckles looks over, was gone. As it turns out Ix had come with the "Marauders" to Sonic's world just so he could steal the Master Emerald. Before the rescue of Knuckles was known, there is a movie at the beginning of the game that tells of how a long while ago Sonic, Knuckles, and Tails had taken part of a plan to destroy Eggman's Egg Carrier. When they take down the Egg Carrier, Eggman goes down with it and is then presumed dead. The disapearence of Angel Island makes Sonic and friends think that maybe Eggman did survive the crash. It is revealed that he did indeed survive the crash and that he is not responsible for the disapearence of the floating island. He is angry that someone else would reprogram his robots. Eggman then tells Sonic and friends that he has "turned over a new leaf" and will help them to be rid of the Marauders. Eggman and Tails build a device to track the runaway island and find that it is in the Metropolis area which has seen better days when rediscovered by Sonic and friends. Sonic and Tails split up into teams when they reach the location of the island. Sonic and Knuckles were on one team, Tails and Eggman were on the other. Now Sonic and Knuckles board a Marauder ship that is just about to take off just in time. When the two reach the island, they see Imperator Ix for the first time. He sends two waves of Marauders which are now called Nocturnus at the two of them. Ix is fought five times during the course of the game.
Ix's plan part 2
After the two Nocturnus waves are fought, Ix gets mad and decides to deal with Sonic and friends himself. This is the first battle with Ix. Ix is the only member of the Nocturnus clan who does not have the life-stealing tech of the Nocturnus with him in any of the battles you have with him. Once Ix is defeated, he will steal the Master Emerald with succession. Once this is done, Angel Island starts to fall. When the island hits the ground, Metropolis, Dr. Eggman's city, is destroyed in the process.
The next Ix sighting
The next time you get to Ix, he'll have been waiting for you. This is evident in when he sends two different colored Gizoids at you, Scylla and Charyb. They are named after two sectors in the Twilight Cage. Once these two are defeated you will eventually find Ix waiting for you for the final four battles to come. In the second Ix battle, Knuckles and Shade fight him. On the third battle, this time it's Sonic and Tails turn. The fourth battle is more of a distraction this time. This time Knuckles is not avialable for he will retrieve the Master Emerald during this fight. Once Knuckles gets back the emerald, Ix gets mad that he cannot go back to Sonic's world now and then summons the power of the Nocturne. Sonic responds by absorbing the power of the seven Chaos Emeralds and engages Ix in combat. Once this battle is over the gang heads back to Sonic's world to find out that they had been gone for years. By that time, Dr. Eggman had already managed to build a massive army of robots. True to every time he promises to "turn over a new leaf" he never kept this promise. After shooting down the main mode of transport for Sonic and friends, the credits begin. Once these roll by you have to replay the whole game again. Fortunately the abilities, levels, and even items you gained are not lost.