Ater is a Fearling, shadow creature born before the Golden Age.
He can mimic human voices and, unlike other fearlings, can take also a human form. He pretty likes it and uses it everytime he can.
He likes to brush against people and yes, he definitely purrs.
(I follow the tag afellowfearling)
((In this gif you can see the first apparition of Pitch in his shadow form. <3 ))