Deerhound

These endearingly shabby dogs are athletic and rather affectionate with an unassuming nature. Their large stature gives them the air of a protector which is perfect for a Patronus. Not to mention the fact they like to form strong bonds.
Written by the harrypotter.com team
“The Patronus is a kind of positive force, a projection of the very things that the Dementor feeds upon - hope, happiness, the desire to survive – but it cannot feel despair, as real humans can, so the Dementors can’t hurt it.”
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