"The existence of Angels has confounded scholars for centuries. There are detailed accounts of their influence, and a page here and there of what they look like, but despite all my attempts they seem unwilling to grace me with their presence! I can only surmise that they appear to those who are destined for great purpose, or to those who are about to make a mistake so monumental, it would threaten the entire fabric of our reality."
-Excerpt from Beyond the Material: Volo's Guide to Extraplanars