Shadow the Hedgehog
Immortal (but he is 51 yrs old)
Shadow is sharp and always on edge, he will accomplish whatever he puts his mind, no matter the danger. He has a friendly relationship with Rouge and this other guy, and with Sonic they have gone from enemies to friendly rivals.
Shadow was created by Gerald Robotnik, to become the ultimate being. He was a step to cure Robotnik's granddaughter, Maria, from NIDS. But the government disapproved of Project Shadow and sent people to go and infiltrate (Space Colony ARK) and to kill anyone there. When they arrived, Maria sent Shadow, her friend, in an escape pod. Before she died, she told Shadow to give people "A chance to be happy". Gerald was driven insane after Maria's death and he programmed the ARK to crash into Earth once the 7 Chaos Emeralds were in it. He programmed Shadow's mind to carry out the plan if he was ever released. 50 years later, the grandson of Gerald known as "Eggman" sought after Shadow as he learned about what his grandfather created, in hope to use him to conquer the world. Shadow, who had sworn revenge on the humans who caused the death of Maria, tricked Eggman, along with Rouge, to collect the 7Chaos Emeralds and thus, make the ARK crash into earth. But Amy Rose triggered the memory of Maria, and Shadow used Chaos Control to force the ARK back in orbit. But he used all of his energy up, and he went crashing towards the ground, presumed dead. Later Rouge discovered Shadow in a tube with his memory lost. He almost forces the humans to destroy him, but they realize he has the heart and soul of Maria. Then with still no memory of his past, he met a race of aliens (called Black Arms). They seem to have known Gerald and they reveal many secrets to him. But Shadow had to do one thing- stop the aliens from taking over the world. He later appears along side Sonic and Silver fighting Mephiles the Dark, and then uncovers the truth about eggman.