Dragons

New dragon concept
Dragons were used by space farers and astral travellers as vehicles, taking them across the multiverse, until after time spent in the different planes, they became imbued with magic, developing in secret their own language, hierarchy and culture. Emboldened by their newfound powers, the dragons overthrew their masters, plunging the mortal realms into chaos. They took charge and descended across the worlds, destroying many and enslaving the rest.
Though all dragons were castrated by their masters, they attempted rituals to create new kin, but managed only to form hybrids and cross breeds. Their descendants still roam the multiverse today.
Dragonborn Scakeskin (Viashino)

Also, many species have evolved after extended exposure to radiation from the fallout of the dragon rebellion and domination. These species tend to be biome specific and come from native species such as owl folk, rabbit folk and then loxodons and so forth. Though not related to dragons, the elders often carry stories of their birth and thus show favour to any dragons or dragonkin they come across, and isolated communities of dragonkin will freely trade with radiation species and vice versa. In more populated areas, where dragon kin are shunned or even hunted, radiation species will harbour them and act in defiance of the law to protect them. Organisations such as the Wayward Plumbers are dedicated to this purpose exactly, sometimes even employing dragonkin in construction jobs to help them save money to relocate. 
Owl Folk Rabbit Folk Fox Folk Elephant Folk (Loxodon) Turtle Folk (Tortle) Snake Folk (Yuan-ti)
Radiation sickness to non-radiation species is commonplace in areas built near dragon burials or activity. Travellers may hear of radiation sickness and deaths following a tomb discovery. Dragonkin are resistant to radiation but not immune, as are radiation species. Rudimentary hazmat suits are constructed using charcoal filters and dragon scale pieces fastened with dragon innards.