"You can control it, Credence."
"But I don’t think I want to, Mr Graves."
-- Percival Graves and Credence Barebone (WFT)
Credence Barebone was the adopted son of Mary Lou Barebone, a fanatical leader of the anti-magic Second Salem Philanthropic Society in 1920s New York.
Along with his two adopted sisters, he would often help his mother and the Second Salemers by hanging up posters, finding places to preach on street corners, and washing dishes in the soup kitchen at New Salem Church (WFT).
In spite of his passive obedience, Credence was abused by the tyrannical Mary Lou, who singled him out for beatings with his own leather belt for the smallest infraction, such as coming home late even though he was an adult. When Auror Tina Goldstein discovered that Mary Lou was abusing her children, she stopped one of the beatings and comforted Credence with a hug, then attacked Mary Lou in front of her followers. That was a bad idea for Tina’s career because every No-Maj at the Second Salem meeting had to be Obliviated. As a result, Tina was demoted from Auror to the Wand Permit Department at MACUSA.
At some point in 1926, evil wizard Gellert Grindelwald (disguised as American Auror Percival Graves) made contact with Credence, displaying affection and revealing that he was aware that Credence had magical abilities. Graves/Grindelwald promised to help him join the magical world someday if Credence would help find a magical child with “immense power” somehow connected to his mother Mary Lou, which he had seen in a vision. Convinced he was the “key” to finding this child, Credence began to study the orphans who came to eat at the church, such as a boy with a birthmark thought to be a “witch’s mark” (WFT). Graves/Grindelwald gave him a necklace with the symbol of the Deathly Hallows on it so he could contact him if he ever found the child.
Eventually Credence must have begun to suspect that one of his sisters was the child sought by Graves because he started searching the objects under the bed of his 8-year-old sister, Modesty, and found a toy magic wand that at first he thought was real. Their mother Mary Lou came upstairs and took the belt in order to punish Credence until Modesty admitted the wand belonged to her. This time Mary Lou would not be able to abuse either child because the belt jumped from her hand, then slithered away, just before a violent Dark magic known as an Obscurus burst forth from Credence and killed her, as well as his sister Chastity, while also destroying the church building. These deaths were in addition to the earlier mysterious death of Senator Shaw, who had called Credence a “freak” while the Barebone family visited his father’s office.
The Obscurus had formed because Credence had suppressed his magical ability all his life due to the teachings of the Second Salemers and the constant abuse from his mother. The power of the Dark energy had grown until he could not control it anymore. Graves/Grindelwald never suspected that Credence was an Obscurial because of his age, since most children with this problem do not survive past the age of ten (WFT).
Graves/Grindelwald found Credence again after the death of Mary Lou, but this time instead of showing friendship he criticized him as a Squib with “magical ancestry, but no power” (WFT). This angered and confused Credence who realized that Graves only wanted to find his sister Modesty, who was young enough to be an Obscurial. Once they found the tenement where Modesty was hiding, however, Graves realized his mistake as the Obscurus once again burst forth from Credence and destroyed the building while attacking Graves, whom Credence realized had simply used him to get what he wanted. Credence and his Obscurus went on a rampage of destruction through New York City, knocking down buildings and overturning cars (WFT).
Both Newt Scamander and Tina Goldstein tried to reason with the out-of-control Credence and help him out of the situation, but Graves/Grindelwald kept interrupting to keep him stirred up so he would cause more destruction. That was Grindelwald’s goal all along – to use an Obscurial like Credence to start a war between the magical folk and the No-Maj. In the end, President Seraphina Picquery told her Aurors to destroy the Obscurus and it was unclear how much of Credence was left still inside it at the time.
He was adopted by abusive fanatic Mary Lou Barebone along with two siblings, so there was no blood connection to the earlier ancestor Bartholomew Barebone except being raised with the same anti-magic obsession. His real mother is unknown but probably a witch since Mary Lou Barebone said "I am not your ma! Your mother was a wicked, unnatural woman!" (WFT).
Immense power as an Obscurial bent on destruction.
Medieval Latin credentia "belief," from Latin credentum / credere "believe, trust"
"Credo" means "I believe" which is the first line of the Apostles Creed, a document of the early Christian Church, hinting at the religious fervor of Mary Lou Barebone who gave her adopted children names reminiscent of those given to Puritan children at the time of the Salem Witch Trials.
"Barebone" hints at the Puritan Sourer legacy Bartholomew Barebone and his family carry on; first, it alludes to the austerity of Puritan sensibilities; second, Praise-God Barebone was an English Puritan of the Commonwealth/Interregnum (the period of English history between the English Civil War and the Restoration of the monarchy, when Puritans basically controlled the government and instituted reforms related to their religious and moral beliefs) who belonged to a sect particularly concerned with Judgement Day and whose name is used in reference to the appointed parliament which immediately preceded Oliver Cromwell being made Lord Protector (Barebone's parliament). (Sources: Wikipedia 1, 2, 3, 4, 5)
From the Web
Credence Barebone on Harry Potter Wiki