the Avengers had just defeated the Zodiac Cartel when Zodaic member Libra revealed that he is really the father of Mantis. He explains that he was a US soldier that fought in Viet Nam who ended up falling in love with a Vietnamese woman who was the sister of Monsieur Khruul and that they had a child together.
When Khruul learned of this he had them burned alive, Libra's wife died however, he managed to escape with his child and found the ancient city of the Priests of Pama who took them in and trained his daughter in their ways, eventually he left.
The Avengers end up having to rush to Viet Nam when they learn that the Swordman, in an effort to prove himself worthy of Mantis' affections flew there to take down Monsieur Khruul. Upon their arrival, they find that Swordsman was captured and tortured until he revealed the location of the temple of the Priests of Pama.
Arriving there too late, the Avengers find that Khruul and his men slaughtered the priests, however Khruul himself ended his own life by freeing a creature known as the Star Stalker, which was the Priests captive.