Although it probably comes as a shock to most folks, I wasn't always a rat. In fact, I didn't become a rat until after I made my MK character a rat. I made Charles a rat because rats were vermin, and I wanted a character whose species led to being ostracized in general. I played up on this in my first cycle, having the other rats in the cellar, and having him being generally ignored by the nobility (hence the rude treatment that Steward Thalberg gave him in 'Errands and Editors'). In the end, him being a rat (as well as Sir Saulius and Lady Kimberly) gave me the opportunity to show nobility in an unlikely form. :-)
Now, I created the other rats because I thought I was going to spend my time more with them when I first started writing. I had several ideas worked out for them, most of which never ended up being written. That's the nature of the given and take in a shared setting.
For the rest of my characters, I won't go through everyone, but some highlights are in order:
Steward Thalberg: I made him an alligator because all the depictions of Thomas and his staff were friendly and noble. I wanted somebody a little stuffy and surly, but wholyl devoted to Thomas. Alligator made a great species for this, great for intimidating and keeping the silly problems from reaching Thoams's desk.
Zhypar Habakkuk: Somebody as odd as him, kangaroo just fit. Plus, nobody else had any, so it made him unique (a position he basically still holds).
Lindsey: In settings where TG is an available option, the vast majority will always be M -> F. M -> F bores me to tears because it's been overdone in every way possible already on the TSA, so I, as I didn't want to write about exclusively furry characters, made Lindsey a F -> M TG. This worked out really well for other story-reasons later on.
Jessica: When I introduced her, almost all Animal-morph Keepers were mammals with a couple reptiles tossed in. We needed an avian, and so Jessica became a hawk. A popular race as far as avians go, and if we'd had more of them, I would have made her something else. But since we didn't, hawk she became.
Father Francis Hough: Phil and I discussed this one. We agreed the Keep had plenty of animal morphs, but I was not going to let Hough be TGed, so AR was the natural choice.
Yonson: Heretofore, on the TSA Lemurs had always been good guys (even if they wielded machine guns and only had four words). I like switching things around.
Yonson's guards: Weyden became a hawk so he could fore a relationship with Jessica. Maud became a woman to have a TG. Two others went AR, and the other two TFed, one into a giraffe because it was odd, and I'd seen a picture of a lemur riding a giraffe somewhere (which happened in 'Liturgy of Blood'!)
Vinsah: One of the few characters whose TF was plot-dependent.
Egland: We only had one cervine that had been used as a main character (Jon Sleeper), and I kind of wanted to write about somebody with antlers, hence elk.
Alberta Artelanoth (Bryonoth): TGed and TFed, this one was completely plot dependent.
The Avery's: Who better to run a village in the trees than a family of squirrels?
Angus: We needed a badger. Big, burly, and somebody that Misha could feel on an even level with.
Mrs. Levins: What's more homey than a hedgehog who bakes pies?
Garigan: At the time I wrote him, there weren't any major mustelids in Metamor Keep.
James: Originally based on a friend of mine who was often a donkey.
Baerle: Opossum's are nifty, and we didn't have any. Actually, she was supposed to be a walk on character, but she surprised me.
Berchem: I mentioned him in 'Declaration of Allegiance' before I named him, so I knew there was a skunk in Glen Avery already. It was a simple matter to make him more important. And his personality was much like his scent. Not everybody who lives and serves Metamor faithfully ought to be a real hero, if you know what I mean.
So I guess most of my characters were the way they were because it just seemed like a good idea at the time, and also, because those species weren't being used yet, and I wanted to try something new. Rats are old hat for me now, but I'd never written one before I started to write Metamor Keep; and I certainly hadn't thought of myself as rat until after Metamor sucked me in. :-)
Dominus vobiscum