Odin here is one of Cade's two massive horses. He is the older of the pair, gentler, and very well behaved generally. He seems to have an idea of what would be best for Cade at times though, and has once or twice physically shoved her in a direction he thought she should go. She curses him for it, but knows when to take the hint. It's all in love, after all. Cade can ride and guide Odin without any tack whatsoever -- she rides him bareback, directing him through paces and directions with just her hands and legs and verbal instructions. Odin is the horse version of the 'strong, silent type,' and sometimes disciplines Loki himself. He comes to her when she whistles a certain way.
Loki, meanwhile, the younger of the two horses, is more rambunctious. He's something like a prankster. He knows better, and will do it anyway. He does know when to behave though, and will listen if Cade tells him something. He just wants to have fun while he's at it. He's vocal, whickering and snorting and whinnying regularly to tell everyone what he thinks. He likes to mouth/lick/'snack' on the hair and clothes of people who try to be around Cade while he's there, and seems to get a kick out of it when they yell -- he especially enjoys picking on Ian. Give him a treat (sugar cubes, apples, the like) though and he'll be a bit nicer. Cade sometimes has to use a bridle with him, just because he occasionally gets distracted and wants to do his own thing. He generally will be properly remorseful when Odin or Cade scold him -- if only for a little while. He also answers to Cade's whistle.
Odin and Loki are of an Aboideauan breed of horses descended from various workhorse breeds brought over to Aboideau millenia ago. They have a build which resembles a cross between Clydesdales and Friesians, but are quite a bit taller/bigger than the largest of those breeds, topping out at about 75-80 inches at the withers on average. They were bred and adapted, evolving for thousands of years, for the heavy duty work required of them on Aboideau. Similarly, they have evolved with coat patterns and colors you would not see in other breeds of horses, often having a tri-color look with marbled spotting (almost like some cats would have).