Orion during Supervised Outdoor Playtime.
It's tough to get a good picture of him for some reason,
so I was quite pleased when I got this one.

From the constellation.  Of course, the constellation was named after the mythological figure, and that fits him pretty well, too.
Other given names considered:  None.
*Bottle*, *Bottle Boy*, Water Bottle.
He ended up with this peculiar set of nicknames after I picked him up once when he was little and commented that he felt just like a hot water bottle:  warm, soft, and a bit squishy.
July 15 (?), 1999
Large, long, and muscular, but on the skinny side for his size.  His weight varies quite a bit according to the season. In the cooler months, he usually weighs between 12.5 and 13.5 pounds (5.6 -  6.1 kg), but he tends to drop quite a bit of weight during the summer.  People frequently question his ancestry, asking if he is part bobcat.  He does have a kind of "wild" look to him, but of course it's extremely unlikely there is a bobcat anywhere in his family tree.  We aren't sure whether he is mostly Manx or possibly American Bobtail.
Orion is a handsome, noble-looking cat.  No one could ever mistake him for a female.  His fur is very fine and soft, as was his sister Andromeda's, and he couldn't quite make up his mind whether to be long-haired or short-haired and so has mostly short hair, but very long guard hairs.
Orion has the nicest, most pleasant-sounding meow.  It is composed of several different tones, which harmonize beautifully and make me wish he would talk more than he does.  He produces full meows, but more frequently simply asks, "Mmmm?" and he almost always says "hello" when we greet him.
Purr:  Moderately loud.  He purrs fairly frequently, but not constantly like his sister.
Biscuits:  Only makes biscuits when nursing.
In case you aren't familiar with nursing behavior in cats, here goes:
A fair number of cats - though I don't have a percentage - never grow out of the suckling behavior they display as kittens when nursing from their mothers.  Some cats will suck on blankets or clothing, some on earlobes or other body parts, and I'm sure others choose other objects. 
Orion has selected my hair as his target and does not nurse on anything else.  I figure I wash it in the morning anyway, so what the hey...  If he wants to nurse in the middle of the night and I'm not positioned properly, he taps me gently on the head with his paw until I wake up and move, or if necessary, pulls the covers off my head.   When he was little, he often nursed in the evenings before bedtime, and if I was wearing my hair up, he cried until I let it down.  The nursing business doesn't do much for his macho image, but he doesn't seem to mind.  He's doing it less frequently as he gets older.
On September 7, 1999, we took Arivaca, who was then our youngest cat, to the vet on emergency hours.  Two employees of the pet store down the road arrived at the animal hospital at the same time we did, carrying a box of six small kittens someone had abandoned behind the store.  The smallest kitten had an upper respiratory infection and needed antibiotics.  We all looked surprised and greeted each other.  I know the pet store employees well, since I go there twice a week or so.
When Arivaca died that evening, we were devastated.  We kept thinking about those little kittens, though:  it seemed like they'd shown up when they did for a reason.  We weren't really feeling ready to adopt, but it seemed it was meant to be.  I made the arrangements with the pet store employees, and Orion and Andromeda came home September 10.  Of course, no one could replace Arivaca, but having the babies around did help us get through losing her.
The smallest kitten in the litter died despite medical treatment, unfortunately.  Two of the kittens were adopted by one of the pet store employees and last I heard were well and happy, and the remaining kitten was adopted by someone I don't know.  Hopefully, he (she?) is doing well, also.
Easy-going, good-natured, and flirtatious.   Orion is rarely in a bad mood and usually acts like a giant kitten.  He is often up and about when all the other cats are asleep. 
Orion isn't as adventurous or outgoing as his sister was, and is quite frightened of people he doesn't know.  Though he loves his Papa, he is quite the Mama's Boy.
When he approaches one of us to say hello and get his head rubbed, he tends to swagger.  Most cats arch their backs, but Orion bends from side to side, swinging his hips back and forth as he walks.  The swaggering can get very pronounced when he's especially happy and I'm sure he wonders why we laugh at him.

The only dark side to Orion's personality is his unwarranted hatred of dogs.  He especially hated Spook, when he was still with us.  Spook was very good with cats and never gave any of them a reason to dislike him.  Orion used to lie in wait on the kitchen counters when Spook came in to eat and swat him whenever he came close enough.

Well, OK...there's one more dark side.  He tends to pick fights with other cats for no particular reason.  His sister did the same thing.  If there was no one else to fight with, they would spat with each other.
Back pain.  See Details.
Carrying things in his mouth; chewing the weather-stripping off the door frames; watching the toilet flush; hunting bugs; shredding paper; nursing; playing in the yard; and playing with dry food (he bats a kibble around the house for a while, eats it, then gets another one and repeats the process).
He was closest to his sister Andromeda when they weren't fighting, but he really does not seek out other cats. In spite of his not spending much time hanging around with Andromeda, when she died, he searched the whole house for her.

Wary but not terrified.