Atlantean is a term meaning "person from Atlantis", and as such the concept of Atlanteans appears mostly in older, more Sword & Sorcery inspired games, or in the OSR games they have inspired. Alanteans are often portrayed as physically and/or mentally superior to other human races from the same setting, and may sometimes survive as the origin of merfolk races, given how Atlantis is generally portrayed as having slipped beneath the sea.
In the Rifts megaverse, Atlanteans escaped the sinking of Atlantis by fleeing into the megaverse. True Atlantean is a Racial Character Class in the sourcebook on the Rifts era version of Atlantis, which has been conquered by alien tentacle monsters called the Splugorth.
In the Dungeons & Dragons 5th Edition setting of Primeval Thule, Atlanteans are a fallen race of hyper-advanced humans whose civilization was annihilated and whose population was devastated when some mysterious magical catastrophe spontaneously erased 9/10ths of their race from existence, due to the obliteration of their homeland of Atlantis. The survivors, many thousands strong, descend from sailors, merchants and colonists, but their bloodline is becoming increasingly watered down by interbreeding with the other human ethnicities of Thule, and after 300 years, their culture is slowly fading from existence.
Atlanteans are fully human, and possess a human range of builds, body types, and features. They form a distinct ethnicity, and can be identified as Atlantean at a glance. They are a tall and handsome people in general, and many Atlanteans are natural athletes. Their skin color ranges from a light copper hue to a deep bronze, their hair is usually dark brown or raven-black, and their features tend to be fine. Their most notable features are light-colored eyes in hues that are rare among other humans: gray, green, an icy pale blue, or even a bright gold. The contrast between the light-colored eyes and the copper or bronze complexion is often quite striking. Because Atlanteans are declining in numbers, more and more have married into the general population of Thule. Classic Atlantean features are becoming hard to find, although the wealthiest and most powerful families are more likely to preserve the old bloodlines.
Despite their faded glory, Atlanteans still believe themselves to be "kings among men"; they view themselves as the smartest, most capable and worthy of all human races, buoyed by the strength of their empire and its centuries of domination, and the fact that they achieved heights of learning, scholarship and arcane lore far beyond those of the other humans of Thule. To this day, they still view learning, both practical and sorcerous, as the greatest of strengths, and strive to live up to the legacy of their fallen nation. At its best, this can make them wise and protective patriarchs and matriarchs. At its worst, they can be stuck-up assholes.
In 5e, Atlanteans of Thule have the following stats:
- Ability Score Increase: +2 Intelligence, +1 Strength
- Size: Medium
- Speed: 30 feet
- Broad Education: Atlantean characters begin play with training in any two Intelligence-based skills. Atlanteans are raised with a love of learning and are encouraged to study any subject that catches their interest.
- Headstrong: Atlanteans gain tactical advantage on saving throws against command, dominate, geas, and hold spells. Atlanteans are willful and are used to having their way; when confronted with spells or effects that threaten to master the will with a direct attack, they are difficult to break.
- Wealthy: Atlantean characters begin play with five times the normal starting wealth for their class, and can purchase common magic items with their starting wealth for 100 gp each. Atlanteans come from wealthy families with a number of heirlooms.
The sunken continent of Azlant is very clearly an Atlantis stand in. True Azlanti are described as having skin that's "olive to pale white", hair that "ranges from deep brown or dark red to black" and eye colors that include a deep purple.
Stats wise they're simple: They're Human, but instead of +2 to one ability score of their choice, they get +2 to all of them. They aren't playable (except as a result of one trap in Shattered Star), but can show up as ancient evil that awakens.
They're also in Starfinder, having established a colony (later independent Empire) off-world that continues to the setting's present. They're dicks and not playable, though the monsters stated indicated the +2 to everything is maintain.