Relatively little is known about John Pizer. He was probably born c. 1850, and was a Polish Jew. In 1888 he lived and worked as a bootmaker in Whitechapel. He was the favoured early suspect of Sergeant William Thick, who had known Pizer for years and who apparently had interacted with him when Pizer had allegedly carried out a series of minor assaults on prostitutes in Whitechapel. Pizer later claimed that his arrest was based on animosity on Thick's part, although Pizer did have a previous conviction for a stabbing offence.
His nickname was Leather Apron, a nickname that was applied to Jack the Ripper in the early days of the killings. This similarity appears to have been the only reason Pizer was associated with the case. The association of the killings with the name can be traced back to early September after the murder of Polly Nichols, and was first put forward in the Manchester Guardian. It does not appear to have been associated with the crimes because of any substantial evidence.
He was arrested on September 10th, 1888, although there was no evidence against him. He was released soon after, when it was determined that he had been out of Whitechapel for two of the murders; during one he was staying with relatives, and during another he was talking with a police officer at the London Docks. Pizer died in 1897