Origins   

A member of the Brethren, Celestial engineered species created for the destruction of other species, Sybyl Dorn was the lone female species among the group sent by the Collector to devastate Earth. Jealously spurned on by the Eternal Sersi's bonding with her fellow Brethren member Thane Ector caused much tension, before things were eventually settled. Not long after though Sybyl Dorn killed by the collector after learning about the nature of her race and similarities with the Earth's Eternals. 
 

Creation  

Sybyl Dorn of the alien race the Brethren was created by Bob Harras. Tom Palmer and Andy Kubert, and first appeared in Avengers Vol 1 #334.