Just as the environment is dramatically different so are the races that inhabit Athas. The same species axist but survivng Athas has changes their role in the world. In addition to the standard races of the Forgotten Realms there are two additional races: the Mul and the Thri-Kreen. Below is a list of the races and the changes from how they are in the fogotten realms:
The Mul are a race of half dwarf, half humans. They have taken on the stature, flexibility and mental agility of the humans and the physical resilience and endurance of the dwarves. Most Muls begin their lives in slavery. Due to their harsh beginnings many Mul grow up with little remorse or sympathy, consequently they are slow to trust and even slower to offer friendship.
The Thri-Kreen are a race of insectoids. 6 Limbed and covered in a chitinous armor. They grow up with a strong group mentality refering to the groups in which they participate as clutches. These can refer to friends, family or teams in which they work. They have an odd perception of the world stemming from their unusual beginnings.
The Dragonborn of Athas were created by one of the Sorcerer Kings to serve as a race of sorcerous warriors. Their number dwindled when they were cast out from their home by their creator. They now live in isolated clans in the wastes. Often they set out into the civilised parts of Athas to further their clans interests or support them in some way. Due to their isolation and focus on helping their clan they are often considered to be avaricious, sly and amoral.
The Dwarves of Athas are similar in stature to their Forgotten Realms counterparts but that is pretty much where it ends. They usually have little or no hair and spend their time entirely overland often sporting a tan and calloused hands from the long days work in the sun. They are single minded in their determination to see a task done. Although they no longer have a specific city to call their home, they keep their culture alive through stories of their once great cities and the traditions that began there.
The Eladrin are rarely seen among the people of Athas and most are unaware of their presence at all, prefering to reside in the Land Within the Wind (Athasian equivilant of the Feywild). Having seen the devastation Arcane magic has caused on Athas they have forsaken the ways of Arcane Magic and now focus more on Psionics. They have a longer memory than most and remember the Green Age before the scarring that has left the world in such a state. They see their civilisation as the last remaining vestage of Old Athas. They guard the entrances to the Feywild with great care. When encountering an Eladrin they are often said to be prideful, haughty, condescending and demanding.
The elves of Athas are a nomadic people for the most. They live in the wastes and travel swiftly by foot. They consider riding a mount to be greatly demeaning but are able to keep pace on foot so rarely require one except when injured. In most of the cities in Athas the elves have a market for trading, these bazaars offer a wide range of goods, most of which were obtained in a less than moral fashion. However even the most officus templar can appreciare the wide range of goods available.
Goliaths are a half-giant species created by the Sorcerer Kings long ago to serve as warriors. Most Sorcerer Kings armies still comprise mostly of these enormous fighters. However some have drifted away from the cities and started tribes in the wastes and wilds of Athas. They are a hot tempered people whos moods can change quickly.
Half-Elves are outcasts for the most part in Athas. More so from their own species than others. They are often loners out for themselves. Self-reliant and fiercely independant, they teach themselves what the need to know to survive. Some half elves are bitter and sullen but most strive to make something of themselves and forge strong, endearing personalities. Quick to make friends and strong willed.
Halflings withdrew from the central regions of Tyr when the arcane defiling began. Making their home in the Ringing Mountains they are a spiritual people who live a tribal existance among the montains and forests there. They have stong links to the spiritual plane but are often seen as savage and barbourous. This is mainly due to their canabalistic ways, seeing all creatures as potential sources of sustenance. Halflings consider themselves not as an individual but as an extension of the race. They were once considered the stewards of all Athas, now they jealously guard the small region they have marked as their own.
Humans are by far the dominant species in Athas and come in a great variety of shapes and sizes. Even within the restricted scale of the Tyr regions humans can be seen to foster traits of the specific area they were born. Humans are also given to have odd physical traits such as changes in skin or eye colour or exagerated features, this may be a result of the powerful magics that were worked on the land. Humans are less numerous in the wastes of Athas than they are in the City States. The chains of oppression that have been holding the land up until now have chafed at the human spirit. But now with the death of Kalak, humans see an opportunity to free themselves and live in a world free of Tyranny.
Teiflings came to be in Athas when Humans made bargains with dark powers to attain the strength to survive in this harsh world. Teiflings are known for their violent and merciless ways. Living mostly in small nomadic bands that raid along the edges of civilisation. Most feel that they have a debt to be paid for the bargain their ancestors struck. This debt can be percieved in any number of ways. Some choosing to pay it off in blood, others in subservience to their tribe and other in acts of honour and virtue.