Amelia Elizabeth Dyer (née Hobley; 1837 – 10 June 1896), popularly dubbed the Ogress of Reading, was a British serial killer who murdered infants in her care over thirty years during the Victorian era.

Trained as a nurse and widowed in 1869, Dyer turned to baby farming—the practice of adopting unwanted infants in exchange for money to support herself. She initially cared for the children legitimately, in addition to having two of her own. Still, whether intentionally or not, a number of them died in her care, leading to a conviction for neglect and six months' hard labour. She then began directly murdering children she "adopted", strangling at least some of them, and disposing of the bodies to avoid attention. Mentally unstable, she was committed to several mental asylums throughout her life, despite suspicions of feigning, and survived at least one serious suicide attempt.

Dyer's downfall came when the bagged corpse of an infant was discovered in the River Thames, with evidence linking back to her. She was arrested on 4 April 1896. In one of the most sensational trials of the Victorian period, she was found guilty of the murder of infant Doris Marmon and hanged on 10 June 1896. At the time of her death, a handful of murders were attributed to Dyer, but there is little doubt she was responsible for many more similar deaths—up to 400 (or possibly more), making her a candidate for history's most prolific serial killer.

Dyer's case led to stricter laws for adoption and child protection, and helped raise the profile of the fledgling National Society for the Prevention of Cruelty to Children (NSPCC), which formed in 1884.

Amelia Elizabeth Hobley was born the youngest of five (with three brothers – Thomas, James and William – and a sister, Ann) in the small village of Pyle Marsh, just east of Bristol, the daughter of master shoemaker Samuel Hobley and Sarah Hobley (née Weymouth). She learned to read and write and developed a love of literature and poetry. However, her childhood was marred by the mental illness of her mother, caused by typhus. Sarah would have violent fits witnessed by her children and Hobley was obliged to care for her until she died in 1848. Researchers later commented on the effect this had on her, and what it taught her about the symptoms exhibited by those who appear to lose their minds through illness.

Hobley had an elder sister, Sarah Ann, who died in 1841 at age 6, and a younger sister, also named Sarah Ann, who died in 1845 aged a few months. An elder cousin had an illegitimate daughter at the time who was later accepted as the daughter of the grandparents, William and Martha Hobley, who were Hobley's aunt and uncle. After her mother's death, Hobley lived with an aunt in Bristol for a time before serving an apprenticeship with a corset maker. Her father died in 1859. Her eldest brother, Thomas, inherited the family shoe business. In 1861, at the age of 24, Hobley became permanently estranged from at least one of her brothers, James, and moved into lodgings in Trinity Street, Bristol. There she married 59-year-old George Thomas. They both lied about their ages on the marriage certificate to reduce the age gap; George deducted eleven years from his age and Amelia added six years to hers—many sources later reported this age as fact, causing much confusion.

Amelia Elizabeth Thomas trained as a nurse. From contact with a midwife, Ellen Dane, she learned of an easier way to earn a living—using her own home to provide lodgings for young women who had conceived illegitimately and then farming off the babies for adoption or allowing them to die of neglect and malnutrition. Dane decamped to the United States shortly after meeting Thomas to escape the attention of the authorities. Unmarried mothers during the Victorian period often struggled to gain an income since the 1834 Poor Law Amendment Act had removed any financial obligation from the fathers of illegitimate children, whilst bringing up their children in a society where single parenthood and illegitimacy were stigmatized. This led to the practice of baby farming, in which individuals acted as adoption or fostering agents in return for regular payments or a single, up-front fee from the babies' mothers. Many businesses were set up to take in these young women and care for them until they gave birth. The mothers subsequently left their unwanted babies to be looked after as "nurse children". Dyer had to leave nursing with the birth of a daughter named Ellen.

George died in 1869, and his wife was left needing a new source of income.