Infinite

"You may call me..... 'Infinite'.... in the brief moments that remain to you."

Infinite is a villain from the Sonic: Fallen Forces Universe. He has an undying hatred for Sonic the Hedgehog, and has sided with the Scientists to see his home burn.

Backstory
Miles "Tails" Prower was once Sonic's closest friend and ally, his 'sidekick' if you will. The two did almost everything together. Many, many times, Dr. Eggman would try to take over the world, and many, many times, Sonic, Tails and their friends would be there to stop him. All the while, however, Tails felt a nagging envy for Sonic. Sonic was always hailed as the hero, but there were many times where he simply could not beat Eggman without the help of his friends. Especially Tails. But Miles managed to control this envy. After all, Sonic was still his friend, and he still was thanked for his contribution, though not as much as he might've liked.

Then, came the dark day that Infinite was born.

There are few details of how it happened, but Sonic's usual nonchalant and cocky attitude got people killed. Lots of people. Sonic made a mistake, and the mission was lost because of it. Eggman pressed that advantage, and in a final, climactic battle, everyone that Tails had ever known and loved - his entire family, most if not all of his friends - were killed. And Sonic? Sonic fled like a coward. Sonic escaped, but only because he could flee the fastest. Tails, meanwhile, stayed and fought.

One eye was burst, his jaw broken, all the skin and most of the flesh burned from his face. The battle left nothing but a mangled, destroyed mash of scars where Miles' face once was. Eggman departed the scene, taunting Tails, the sole survivor, by saying he was too worthless and weak to even finish off.

And there, in the ashes of his home, surrounded by the burnt and mutilated corpses of his friends, Tails made a proclamation to the void, a statement that none but the dead would hear: "I AM NOT WEAK!"

First Arc (Science Begets Death)
Infinite joined the Science Alliance to help destroy everything Sonic cares about. Only to realize Sonic is already, for the most part, broken. Dammit.

Second Arc (World's Break)
After a confrontation and reveal of his backstory, Infinite lets Robotnik and Sonic duke it out (which ends kid of quickly, to be honest) and gives Sonic a healing factor. Now, Sonic can't die until Infinite is dead.

Relations
Sonic - Hates with a passion

Everyone else on either side - literally couldn't give less a fuck about anyone, or about the war itself.