Aasimar
Aasimar are a player character race in Dungeons & Dragons editions 2, 3, 3.5, and 5 (via the DMG) and in Pathfinder. They are counterparts to Tieflings and Genasi, being mortals who bear the blood of Celestials - the residents of the Upper Planes - in their lineage.
Aasimar originated in the Planescape setting, as with their counterparts. Like the genasi, though, they came after the setting was initially released; the corebook for Planescape introduced only the tiefling, githzerai, and bariaur races.
Aasimar are basically tailor made for people who want to play the various Good branches of the Alignment tree, especially as Clerics or Paladins, since they literally have living good in their veins, though, as with tieflings, playing around with the concept was popular.
In 4e, in an attempt to avoid "grid-filling", aasimar never made it over. Instead, devas, beings who are former angels banished or voluntarily departed from the Astral Sea to live amongst mortals, took their place. Which filled the grid for good-aligned supernatural race as a counterpart to tieflings.
In Pathfinder, it's noted that a lot of Aasimar actually tend to go evil either because superstitious yokels tend to pile on emotional trauma and guilt until they snap by constantly harassing them for "blessings" that the aasimar can't actually give, or because they realize everyone automatically expects them to be capital-G Good Guys/Girls and so they can easily manipulate people. This is yet another way in which Pathfinder likes to present itself as the GrimDark D&D equivalent setting. They can have lots of different possible starting types, depending on which kind of celestial they descended from. Interestingly, supplements explicitly encourage white-hot holy-on-unholy action by stressing the odd sense of kinship most aasimar feel for their similarly-bullshit-cultural-expectation-wracked fiend-blooded counterparts.
Aasimar returned to 5e in the DMG as the sample race for showcasing the "build a race" rules. They're basically Tieflings flipped to a more Celestial aspect, complete with sharing the same +1 Mental Stat (Wisdom, for Aasimar) +2 Charisma bonus, Darkvision, Damage Resistance (Necrotic + Radiant) and spell-like abilities at level 1 (Lights), 3 (Lesser Restoration) and 5 (Daylight) format. They were recently voted one of the three most-popular races for a new D&D expansion to create in detail.
