The Ovoids are a highly evolved species. They are very peaceful and technologically advanced. The Ovoids have developed a body transfer system which places their minds in fresh new bodies when they are near death, making them nearly immortal. 
  
In space, they happened upon Doctor Doom and shared their technology with him. When they left him back on Earth, he successfully used their body transfer technology to switch bodies with Mr. Fantastic. 
 
When Galactus came near their worlds, they prepared to battle with him to protect their planets. They successfully killed Galactus' herald, Air-Walker.