The original DADA teacher was actually going to be the Bloody Baron.  I didn't want to write an OC (not because I can't but because I was trying to approximate Book 6 as much as possible and my own OC would contradict that too much).  But I thought that no wizard would possibly consider the DADA job by this point anyways, so another ghost teacher seemed like a good idea and it seemed interesting to have the Bloody Baron since we really don't know much about him.

But then I realized I would be contradicting canon even more if I didn't have a new character as the DADA teacher, so I invented Ramsey.  I was very careful with him though.  I had read several theories about DADA teachers and Ramsey fits these patterns.  First, someone has suggested that there is a pattern to the type of teacher (good, bad, or evil) and Ramsey's type fits in this sequence.  For those that are wondering if he's good or evil, you'll have to find this theory - I'm not giving that away yet.  Second, Harry had to hear of him before arriving at school, which does happen in Lily's diary (although Harry doesn't know it). 

Then I established a history for Ramsey - parents, background, talents, fears, desires, appearance, etc.  I made sure that he had weaknesses as well as strengths.  He also had to be an entirely different character, not quite like any other we've met. 

So here are some of the random details I've written about Ramsey (no spoilers).

Birthday: March 11, 1958
Appearance: Dark Brown hair, tan skin, blue-grey eyes, angular face, strong chin, lock of hair falls gracefully over one side of his forehead.  Looks younger than his years. Very handsome. Dresses impeccably but with odd touches - robes are lined with gold threading which gives them a foreign Middle Eastern look.  They're lightweight robes made for warmer climates (remember he arrived straight from Egypt) that are preferable to the heavy wool robes the rest of the teachers wear.
Personality traits: Mysterious, intelligent, charming, brooding, quiet, loner- he rarely eats meals in the Great Hall.
 
History (partial without spoilers): Although he was Head Boy, he left school as soon as he'd finished his NEWTs, just after the blowout with...the character who you know he was friends with by the end of chapter 19 (don't want to spoil it for anyone who hasn't read it yet).  He was very talented and could have had any job he wanted, but he vanished without a trace only to be heard from in various exotic locations over the years. His Occlumency talents were learned in his formative years rather than his later years.
I started this portrait of him a while back, unfortunately it's not quite finished but you get the idea.
<img src="http://i2.photobucket.com/albums/y22/Beaustylo/ramsey.jpg" alt="Image hosted by Photobucket.com">