Tieflings are a relatively young race, only about twelve hundred years old. Once, they were the human nobility of the Kingdom of Falwyth, but, during the Black Fire War, they made deals with devils to gain power and advantage in the war against the Dragonborn. As a mark of their pledge of service, the tieflings were changed in shape and color, becoming markedly different from the humans they now ruled.
Almost all of the tieflings that stayed in Falwyth were wiped out, but some of the younger nobles, feeling that their fathers and mothers had gone too far, departed with the humans who became the Summerlings. The peaceful tieflings who traveled to Aldorath abdicated their rule in favor of humans who would better serve the people of the new Kingdom of Summerlund.
Only the most self-deluding of todays tieflings will try to pretend that they have not been affected by their ancestral transformation. Tieflings can be very charismatic and personable, but there remains the taint of something inhuman about them – a hint of wrath and hunger. They tend to shun positions of authority, perhaps in fear of the corruption their ancestors succumbed to.