The Rending of Palaghast
The birth of an Aasimar is rare and seen as a blessing from the Eight. Born to Human parents, the Aasimar offspring are quickly taken from their home and moved to the capital cities of their birth Domain. There they are brought up as stewards of the Solar. Most Solar opt to use Aasimar in their care as spokes people, sending them in their stead to announce decrees and edicts.
An Aasimar takes on appearances and aspects of the Domain they were born in. Vivo-Aasimar are tall, statuesque, fair haired, and athletic. Malseren-Aasimar tend to be moody, but excellent crafters. If there are any Morto-Aasimar, they have yet to be seen.
An ages old argument has surrounded these celestial beings. Are they born due to being in such close proximity to the Solar? Or do they Solar leave their palaces in the secret of night, to release their passions? Many find the second belief blasphemous. It is sufficient enough that the holy nature of a Solar can sometimes be transferred to its subjects.
Refer to the DMG for base stats. The Volo's Guide to Monsters has alternatives that we can discuss if you chose this race. In a given party, only one person can be an Aasimar due to their rarity.