General knowledge: The TMNT natural leader, serious, spiritual, religious, fast thinker, perfectionist, balanced, calm when needed, bossy, fights with Raphael, is a devoted ninja and uses katana blades as his weapons.

Leonardo is the unofficial leader of the TMNT, Splinter's star pupil, and possibly his favorite, (which would certainly explain the origin  of the long-standing Leo/Raph conflict.) Leo takes it upon himself to serve as big brother, keeping the others focused on tasks, and attempting to create order and enforce discipline.
He tends to take responsibility for their shortcomings, as well as his own, which gives him some serious problems with self doubt. Although Leo can be hard on his brothers, he's harder on himself than anyone else. The most commited to the art of Ninjitsu, and Splinter's teachings, Leo is the most principled and honor-bound, and in Splinter's absense, he is the spiritual center of the four.
He does not like to let his emotions go to extremes. He also does not care to lust for women and food... openly.
On the other hand, Leo does have a soft side to this faultless leader image.  It times of need, when someone needs caring, he can open up more to show his understanding and compassion.
He is sensitive, but like Raph, would rather hide behind a "wall".  This "perfect role model" image of himself around his brothers.
Probably the most skilled ninja, especially when it comes to meditating. Leo prefers a fair fight, hates guns, and enjoys classical novels and poetry.

What I think: What can I say about Leo? For starters, he's the turtle most of us love to hate.
Sure, I didn't like him much before either, but lately, after reading Mirage and GreenWilloW's famous (famous among TMNT-fans online) stories where Leo gets pretty much covered, I've had a change of heart.
We see another aspect of Leo, not just the bossy big brother-- of course we get a little of that too, but we see the heroic side of Leo-- true of heart, honorable, prepared to sacrifice himself...and I must admit the guy's growing on me-- and fast! He does have his own little charm. Sure, the charm's not flowing over in the bucket of Leo's personality, but it would be enough to clench anyone's thirst!
Leo's what I would call "a mother-in-law's dream", too-- but that's not necessarily a good thing. Heh.
Well, anyway, Leo is the party pooper, and that's probably why fans generally like him the least, but after all, we do need someone to drag us back into reality now and then. Leo's intentions are good, and I think that all of the turtles know so, even Raph.
He's a good guidance when Master Splinter is away, and he fights to make them stick together.
One thing I've learned, however, is that just like when it's that rare time when Raph shows his emotions, it's just as blissfully endearing when Leo loosens up from time to time.
It's feels like a blessing when you get this guy to smile. By the way, although I would hesitate to admit it, I do admire Leonardo highly for what he does. I wish, for one, that I had his ability to concentrate.

Me and Leo, by me
 

Is it true that you can tell a lot about a person just by their handwriting?
 

Hey! Why not visit GreenWilloW's Leonardo Shrinesite? Click on the pic of the blue-boy above! ^_^

If you feel I have missed any vital information on this character, (besides stats, you know, weight and such) please don't hesitate to mail me. lolascubish@hotmail.com