Celestials are from one of the Celestial Planes, also called the Upper Planes in some cosmological models, and the cosmological counterparts and antithesis to fiends. While the term "angel" properly referred to a subset of celestials, those on the Material Plane helped by any celestial being might claim to have been "visited by an angel". All celestials, regardless of species, station or creed, were united in one thing: good will. Celestials were commonly thought of not just as "good beings" but embodiments of "all that is good"; the very essence of it suffused every bit of their being, body and soul.
Celestials performed many roles across the multiverse. They were divine heralds who brought the messages of the Upper-planar gods to those who needed to hear them and agents of good who acted outside the divine mandate. They were the punishers of the wicked and ministers to the needy, protectors of the innocent and liberators of the enslaved. They were both wanderers who roamed the planes to find the good in all things and guides who led champions in their quests against evil. They were the embodiments of the multiverse's purity and the pinnacles of benevolence and valor. They were all these things, but as a group, they were champions of the betterment of the cosmos who encouraged the spread of harmony and freedom, both for individuals and for societies. They always acted for the utmost benefit of others, to inspire charity, mercy, and helpfulness in turn, and bent their tremendous cosmic influence to the support of good and thwarting of evil.
Celestials were beings of magnificent, empyreal aspect, but that aspect varied widely in appearance. Whether it was stately or wild however, virtually all were comely and beautiful to behold in their own unique ways. Even those known to have strange or frightening appearances never seemed evil.