Devotee of Vishnu is one who recognises Vishnu as the supporter of the entire existence. It is not the body that determines if one is a Vaishnava or not. The Prahladahad had abody of rakshasa, but is a great devotee of Vishnu. Not only a rakshasa, even a few animals such as Jatayu, Gajendra
Source: MandasaTemple-Chinnajeeyar
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