Manuel Blanco Romasanta was born on November 18, 1809, in Regueiro, Esgos, Ourense, Galicia, Spain. His given name at birth was Manuela, reflecting a different understanding of gender in the past. Romasanta was of small stature, standing between 4 feet 6 inches and 4 feet 11 inches tall. He had blonde hair and was described as having a tender appearance.

In his early life, Romasanta worked as a dressmaker. He later got married but was widowed just a year into his marriage. After his wife's death in 1833, he became a traveling salesman. He started his sales career in Esgos but eventually traveled throughout Galicia and Portugal. Romasanta also served as a guide for travelers crossing the mountains to Castile, Asturias, and Cantabria.

He had a varied work history, taking jobs as a cook, coir maker, and weaver. During his time in the village of Rebordechao, he became known for helping with the harvest. His friendly demeanor towards the women in the village led some of the local men to view him as effeminate.

Manuel Blanco Romasanta was charged with multiple murders during the years he worked as a traveling salesman. In 1844, he was first accused of killing Vicente Fernández, who was trying to collect a debt from him. He was found guilty in absentia and sentenced to ten years in prison. Fearing imprisonment, Blanco fled and lived in hiding. He resurfaced under a false name, Antonio Gómez, and began living in a small village.

In the years that followed, several women and children who traveled with Blanco as a guide began to vanish. Their disappearances went unnoticed at first because Blanco sent letters to their families, claiming they had reached their destinations safely. Suspicion grew when people noticed him selling clothing that belonged to the missing individuals. Rumors also circulated that he was making soap from human fat.

By 1852, a complaint was filed against Blanco, leading to his arrest in September of that year. He was charged with tricking women and children to murder them for their fat. When brought to trial in Allariz, he confessed to thirteen murders but claimed he was suffering from a condition called lycanthropy, which caused him to transform into a wolf. This unique defense captured public attention.

During the trial, forensic evidence cleared him of four murders attributed to wolf attacks. He was convicted of nine murders, with the remains showing signs of being butchered. On April 6, 1853, he was sentenced to death by garrote and ordered to pay compensation for each victim. However, after appeal, his death sentence was commuted to life imprisonment in 1854 due to a request from a French hypnotist who believed in his supposed condition.

Romasanta was transferred to a prison in Celanova, where he was reported to have died on December 14, 1863. Accounts of his death vary. Some say he died of illness, while others suggest he was shot by a guard. Eventually, evidence emerged indicating he might have died in Ceuta prison from stomach cancer. Romasanta remains known in Spain as "the Werewolf of Allariz" due to his gruesome acts and unusual defense.