I've been checking www.jkrowling.co.uk and to my great amusement I found this on the FAQs
http://www.jkrowling.com/textonly/faq_view.cfm?id=49 What is the significance, if any, of Mark Evans?
I couldn't answer the poll question before now, because I've been making arrangements to take my family into hiding. It takes time to arrange fake passports, one-way air tickets to Bolivia and twenty-four hour armed security.
Why should I resort to such desperate measures? Because after you've heard this answer, I'll have to disappear for my own safety.
Now before I get down to it (you can guess what's coming, can't you?) I am going to put up a feeble pre-emptive defence. Firstly, you were all spinning highly ingenious theories about Mark Evans, so I thought that you would welcome the chance to hear the truth about him. Secondly, I tried hard not to raise hopes or expectations by adding the crucial words 'if any' to the question. Thirdly... there is no thirdly. I'm just killing time.
(Takes deep breath)
Mark Evans is... nobody. He's nobody in the sense that Mr. Prentice, Madam Marsh and Gordon-Dudley's-gang-member are nobodies, just background people who need names, but who have no role other than the walk-on parts assigned to them.
(Checks that Neil has immunized the dog and that Jessica has packed her Gameboy, and continues)
I've got nobody to blame but myself. Sirius Black, Mrs. Figg and Mundungus Fletcher were all mentioned in passing well before they burst onto the stage as fully-fledged characters, so now you've all become too clever, not for your own good, but for mine. The fact is that once you drew my attention to it, I realised that Mark Evans did indeed look like one of those 'here he is, just a casual passer-by, nothing to worry about, bet you barely noticed him' characters who would suddenly become, half way through book seven, 'Ha ha! Yes, Mark Evans is back, suckers, and he's the key to everything! He's the Half Blood Prince, he's Harry's Great-Aunt, he's the Heir of Gryffindor, he lives up the Pillar of Storgé and he owns the Mystic Kettle of Nackledirk!' (Possible title of book seven there, must make a note of it).
Then why - WHY - (I hear you cry) - did I give him the surname “Evans”? Well, believe me, you can't regret it more than I do right now. “Evans” is a common name; I didn't give it much thought; I wasn't even trying to set up another red herring. I could just as easily have called him 'Smith' or 'Jones' (or 'Black' or 'Thomas' or 'Brown', all of which would have got me into trouble too).
What else can I say? Many of the theories you presented were highly plausible. If you knew how often I've checked the FAQ poll hoping that one of the other questions might edge into the lead...
Well, that's that. The car with false license plates is at the door and I've got to glue on my goatee. Goodbye.
I also love her because of the books of course, but this is so funny. Especially about the possible title of book seven. By the way
wouldn't Dumbledore in the portrait in the Headmistress' (this sounds so weird) office be able to explain everything? The main question being: did Snape kill him because he asked or is Snape a bastard and a traitor?