The collective being called Over-Mind seemed intent on staying with the Defenders as it transitioned from a non-team into a "new" group. Yet the character inexplicably vanished from the series after Defenders #122 … just before the debut of Cloud in #123.
Not until #149-150 did the New Defenders learn of the intertwining events that transpired between those two earlier issues.
When stars in an area of space began to disappear, a cloud of mass from a sentient nebula journeyed to Earth in search of help. Over-Mind sensed the nebula's thoughts and traveled into the void of space to investigate the phenomenon on his own.
New to Earth, the sentient Cloud tried making contact with a young couple, Carol Faber and Danny Milligan—only to witness their automobile skid off the road and crash. The accident left them both comatose. Psychically traumatized, Cloud acquired the paranormal ability to assume the appearance of the two humans (alternating between female and male forms), while forgetting its own true nature.
Dedicated to the definitive superhero non-team.