Rumor was one of several 'special' children born randomly from mothers who had shown no signs of pregnancy. He (along with six others) was raised by Reginal Hargreeves to save the world.
Rumor was created by Gerard Way and Gabriel Bá. She first appears in The Umbrella Academy / Pantheon City / Zero Killer #1. Originally in the creation process the Rumor was absent in the initial development of the Umbrella Academy characters. When she was first conceived by Gerald Way she appeared more feline in appearance, dramatically different visually from her finished look and appearance. She also went through a stage of having several R and question mark icons along her suit as well as darker curlier hair. All before her finished look with shorter violet hair.
Major Story Arcs
Like the rest of the Academy, The Rumor was born from a random unknown women along with 41 other children at the same time. Knowing that she and the others were special Sir Reginald Hargreeves set out to find as many of the children he could find. He could only find seven of them, one of which, was Allison "The Rumor" Hargreeves. She lived with her, now, 6 brothers and sisters with their adoptive father in a home they knew as the Academy.
Her life was dysfunctional much like the rest of the Academy. Reginald was not the ideal father figure, he tried to teach them how to use their powers as well as when and why they should use them. But this came at a cost for Allison. She was known to use her powers to disobey and live a life she wanted, but her punishment was her father's attempt to have her killed.
Eventually, Rumor left the academy and started a family. Her marriage failed, and she went back to her siblings at the Academy following Reginald's funeral.
Reluctantly, she turned back to super-heroics as her sister Vanya went on the rampage as the White Violin. When Rumor tried to stop her, the White Violin cut her throat, completely severing her vocal cords.
Rumor survived, but she no longer had her powers. It was not until much later that she got them back. Working with 00.05, Rumor's powers were restored so she could kill President Kennedy. She was forced to do this by the threat of the time-travellers killing 00.05's mother...who also happened to be Spaceboy's, who Rumor is in love with.
When Spaceboy heard what Rumor had done he fled to the jungle, to live away from it all.
Anything that Rumor says becomes truth. As an example, when the Umbrella Academy needed the area around the Eiffel Tower cleared as so to ensure the safety of the public and groups of bystanders near by, she exclaimed loudly to them, that she had heard a rumor that Musee D'Orsay is giving away many of its finest paintings as well as serving crepes, this causing the crowd to leave in excitement also making the rumor true. The extent of her ability is unknown.