What is Blackwing?

[Bulldog Psion]

Familiars have been part of the lore of witches, warlocks, and wizards for centuries. Black cats, toads, ravens, homunculi, imps, blah blah. I'm fairly sure there are even treatises written on the subject by various witchfinders and the like. Many of the animals were probably actually just pets taken as "proof" of sorcery by various power-mad loons.

The D&D familiar is an attempt to port this concept over to a game format, minus the demonic elements frequently present in the original concepts.

So, if you're looking for the reasons behind familiars existing, you're going to need to look far beyond D&D into the distant mists of real-world myth.

Here's an introduction if you're curious:

http://en.wikipedia.org/wiki/Familiar_spirit