An elderly man, with a long, flowing beard left Harry on the doorsteps of Four Privet Drive. This man did not recognise the true nature of his mother's sacrifice, and sought only to acquire a perfect weapon based on a false prophecy. As well as warding his home from wizard kind, he cursed Harry's relatives to be uncaring.
However, he didn't take into account either the nature of Lily's sacrifice, or his true heritage. To save her son, she bound her life force to his, and left her body voluntary before she was hit with Avada Kedavra. Her life force took the hit and transformed into a shield for the curse and bound her to his dreams. James rather than leaving his best friend stayed with her, and after about a year they were joined in their self-appointed task by the last trinity. They became his dream guardians. For a waking companion he had a temple snake that had been enchanted by Lily into the form of a silver and emerald torque that grew with him. Part of his protection lies in the snake, and it is mentally linked to Lily so he can communicate with her.
Harry has been raised as Raven Octavius Rowain Argentclaw, the pureblood master of two ancient Slytherin lines. With the others aid he left Four Privet Drive at the age of five and was moved into the family manor by a combination of his dream guardians and house elves. He looks nothing like James Potter. A little judicious tampering on the trinity's half resulted in Raven being added to Hogwarts and the Ministry's paperwork.
He knows what it means to be a pureblood and one of the trinity of mages. He has a thorough grounding in law and politics. He can wield a range of magics all wandless, and a few forbidden including his secondary animagus form. He knows all his prophecies, and those whose content is possibly connected to him. He doesn't trust Dumbledore though his meditation and occulmancy skills allow him to shield that. He knows full well that Sirius is innocent and he has his suspicions about other things.
Letters about Hogwarts
He received only the letter as Raven Octavius, which he automatically replied to. With the aid of his guardians they finished developing his external appearance. With the dint of much magical manipulation his scar was moved from its rather prominent position to a messy scar on his hip that it blended into neatly. His hair was still black, but down to his lower back and streaked with white, green and yellow. His eyes were a very dark green with a silver edge to his pupil and he didn't need glasses. He was a tall boy with a reasonable physique for an active eleven year old.
The Dursleys were punished for losing Harry, but they were unable to trace him, and so he was presumed dead.
Diagon Alley
As a pureblood heir, he required no teacher escort. Instead he had his snake Corvax, who with Lily and James aid guided him around Diagon Alley. At their orders he had the best of everything, including weapons both magical and non-magical. When he ran into Draco in Madam Malkins the trinity bond clicked and he found one of his bond mates. He introduces himself by name and befriends Lord Midnight. His first wand is the familiar holly and phoenix feather, and Ollivander addresses him by his full title.
Platform 9 ¾ and the Train Ride
Raven easily accessed the platform and ensconced himself in an empty compartment and warded it according to his mother's instructions, his top of the range trunk shrunk in his robe pocket. The moment the train started he flicked his favoured foci, an ornate dirk with a basilisk fang core from its sheath and sliced his finger and began to chant a complex parsel spell. Sitting back and healing his finger, he waited a few moments and dropped the wards. Two minutes after he did so Draco joined him and they sat and ate Chocolate Frogs and talked about Quidditch. Neville's toad managed to get into their compartment and a bushy haired girl came searching for it. When she opened the door he felt the other side of the bond stabilise, and silencing Draco, handed her the toad.
The Sorting
The hat sang its traditional song and the sorting began. Hannah Abbot ... ... Hufflepuff!