Hogger is actually a woman!
Yes, you read it right! Hogger is a woman!

But how? why? how come?

It's actually pretty simple. Let's start with the basics:

Hogger is a Gnoll;
Gnolls are a species of humanoid hyena people;
Hogger is brown and spotted;
Hogger is his tribe's Chieftain;
Gnoll society is organized entirely around might. The strongest and deadliest gnolls ascend in the tribal order to become the leaders, while the weaker gnolls soon become food for the rest;
Hogger is described as "A huge gnoll who overpowered all attempts at his capture";
Spotted Hyena is one of the few mammal species where the females are bigger, stronger and more aggressive than males. They are brown and spotted;

Ok. But Questgivers and Warden Thelwater call Hogger using the pronome "he", so Hogger must be a male!

WRONG!

Spotted Hyenas actually have another particularity concerning gender. In this species the female has a pseudo-"male genitalia". I won't get in details here but you can learn about it on wikipedia or googleing it. The fact is that the only way to know the difference is by looking very close, as the female's is actually bigger than the real thing!

So: Hogger was big, strong and had a... you know what. Questgivers just assumed he was male!

There you have it, boys and girls. In my endless pursuit of the TRUTH, I have reached the conclusion that Hogger is a woman!