Other than Joey and Topthorn, most of the horses in War Horse are pretty flat characters. But they serve to show that, just like people, different horses have different personalities.
Kind old Zoey bookends the tale; she's the first horse Joey meets and the last one we see him working beside. She's a calming influence. Joey often feels that the "kindness and sympathy from that old mare [...] cooled [his] panic and soothed [his] spirit" (1.4) Even though Joey was named after Zoey, Joey is fiery and feisty where Zoey is calm and collected. They complement each other well and work together fabulously, but Joey never has the same regard for Zoey as he does for Topthorn. Joey must like his horses the way he likes his coffee—bold, black, and strong.
Coco "had the nastiest temper of any horse [Joey] had ever met" (12.4). If Joey hadn't been raised by Albert, ridden by Captain Nicholls, and tended to by Trooper Warren, and instead had been beaten, broken, and abused, you'd end up with Coco. This is only speculation on our part, though, because poor Coco only lives for four pages before being killed by flying shrapnel.
Oh, the Germans and their goofy names. Heinie's the BHOC (Big Horse on Campus) when Joey and Topthorn join the German regiment, but Joey and Topthorn soon outpull Heinie and get promoted to the front of the pack. Heinie's also calm and collected, but Joey's varied résumé as both war horse and farm horse gives him the upper hand. Unfortunately, we don't get to know Heinie, as he perishes along with Coco four pages after being introduced, showing us that, in war, death can come at any time to anyone.
Now we feel bad for laughing at his name.
The two Haflingers are the pretty boys of the group. We'd love to say that these blondes have more fun, but there is no fun during the war. Even though they're all a part of the same group, Joey doesn't befriend the Haflingers because he doesn't have the same respect for them as he does for Topthorn. They flounce around and have trouble pulling their own weight, often lagging at the back of the back. Joey has no problem helping them, though, showing us his kind and generous nature.
Being at the back of the pack has its perks. Though Coco and Heinie and Topthorn perish, the Haflingers survive. What do you think happened to them after we last saw them fleeing into the woods?