Loki

The other horse was a chesnut mare. The builder knew she was a mare immediately—he did not have to look between her legs. Every line of her, every inch of her, everything about the chestnut was female. Svadilfari wheeled as he ran across the meadow, then he slowed and reared, and neighed loudly.
The chestnut mare ignored him. She stopped running, as if he were not there, and she put her head down and seemed to be cropping the grass as Svadilfari approached her, but when he was within a dozen yards she began to run from him, a canter that became a gallop, and the grey stallion ran behind her, trying to catch her, always a length or two behind, nipping at her rump and tail with his teeth, yet always missing.
They ran across the meadow together in the creamy golden light of the end of the day, the grey horse and the brown, sweat glistening on their flanks. It was almost a dance.
The builder clapped his hands loudly, and whistled and called Svadilfari's name, but the stallion ignored him.
The builder ran out, intending to catch the horse and bring him back to his senses, but the chestnut mare seemed almost to know what he intended, for she slowed and rubbed her ears and mane against the side of the stallion's head, and then ran, as if the wolves were after her, towards the edge of the forest. Svadilfari ran after her, and in moments they both vanished into the shadows of the wood.
The builder cursed, and spat, and waitched for his horse ro reappear.
The shadows lengthened, and Svadilfari did not return.

[...]

Strangely, for it was most unlike him, Loki was not around to be praised for his part in luring away the horse Svadilfari. Nobody knew where he was, although there were those who spoke of a magnificent chestnut mare seen on the meadows beneath Asgard. Loki stayed away for the best part of a year, and when he showed up again, he was accompanied by a grey foal.
It was a beautiful foal, although it had eight legs instead of the usual four, and it followed Loki wherever he went, and nuzzled him, and treated Loki as if he were its mother. Which, of course, was the case.