Tenebrae is a being from another universe that is part of the Mergence, a group mind. She is sent to Earth prior to the Mergence's arrival to get everything in order for the absorption.
Her task is to remove the Silver Surfer from the equation which she does with the help of the Coroner. She first puts him in a machine called the Weaver and implants dreams in him. She does this in the hopes he can be made into the ultimate weapon for the Mergence. But she fails and sends him to the Macroverse. She keeps Alicia Masters protected by a robot known as Cy-Phyrr 4 in case Alicia needs to be used against the Surfer.
She prepares for the Coroner to become one with the Mergence and thus be able to absorb the life on Earth. But the Surfer escapes the Macroverse and thwarts the attempt. This separates Tenebrae from the group mind, which leaves her in fear and doubt for the first time in her memory.
She travels to the Microverse to find Cy-Phyrr 4 and Alicia to continue her plans. She is captured and tortured by Psycho-Man. She is eventually rescued by the Surfer, but turns on him. She is now an individual and used to thinking for herself. She forms an alliance with Psycho-Man.
But the Mergence has arrived and merged with the Coroner. It demands her death and refuses to take her back into the Mergence, being tainted with individuality. She and Psycho-Man attempt to defeat the Mergence but this is stopped by the Silver Surfer. She and Psycho-Man are seemingly killed in the resulting explosion.