Hailing from the planet Varna, the Space-Wolves have evolved in a harsher climate than Earth. They look a lot like the wolves they are named after - coarse fur, long snout, pointed ears and bushy tail - the difference being they walk on their hind legs instead of all fours.
The harsh climate and stronger gravity of Varna have given the Space-Wolves higher strength and vitality than earthlings, and they seem to be able to shake off some attacks that would knock others down. They've never been able to adapt completely to the earth environment and because of this, their balance and earthly common sense are a bit diminished.