When Hephaestus returns to Olympus after being thrown out by Hera, some authors/artists portray him as riding a donkey:
Is there any reason why he rides a donkey? Why not a horse or a turtle?
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It seems, according to Theoi.com, that Hephaestus' animal was a donkey, but nothing on why. My own thought is that it, like Hephaestus, was a worker rather than a warrior.
He may have ridden it on his return to Olympus to show that he came in peace, as riding a donkey could symbolize peaceful intent.