(Homebrew by Keith Baker from the book "Exploring Eberron". Due to the commercial nature of the homebrew, it'll be provided if a player wants to play this race.)
Some people think that the hyena-like Gnolls, due to beeing descended from demons and even having demonic blood, are inherently evil. However, while they do tend to be quite bestial and animalistic, and their especially feral tribes have... interesting... reproductive methods... Gnolls can genuinely become decent, albeit quite slobbery and unruly citizens of humanoid settlements with care and time. Gnolls that either were raised away from their culture that infamously worships the demon-lord Yeenoghu, who come from tribes that simply denounced their culture, or individuals that left their religion and demonic blood and went into self-imposed exile can and will often break away from their violent urges and become great mercenaries and in some cases even Knights. The legendary knight Sir Kragh of Lugh, who helped liberate the Lordship from old Albia, was said to be one such Gnoll. Gnolls can be found pretty much anywhere, in at least some quantities, but have their origin in El-Batok, where some more peaceful tribes also make their home.
Despite there being comparatively peaceful Gnolls, those that follow Yeenoghu have started to become more and more monstrous over the past few decades, resulting in many gnoll tribes taking on fiendish properties; to the point where they can almost certainly be considered fiends themselves.
Gnolls typically age very quickly, reaching maturity at Age 5 and living to be about 30 years old, and they remain spry and vigorous until the last few days before dying of old age. Interesting to note however is that Gnolls living in humanoid civilizations, especially those adopted into Ree-Mai villages, tend to live nearly twice as long, and rarely even approach the usual life expectations of Humans.