Avengers Vol.1 #14
In order to save the Wasp's life, the Avengers seek out the help of Dr. Svenson, only to find he's been replaced by an alien from the planet Kallu.
First Printing: Mar 1965
Writers: Stan Lee, Larry Ivie and Larry Lieber
Art: Jack Kirby, Don Heck, and Chic Stone
Cover: Jack Kirby and Chic Stone