Cosmo Alexander was the son of the Aberdonian painter, John Alexander. He was named after the duke of Gordon's son, who in turn had been named after his Italian godfather. Throughout his life Cosmo Alexander worked as a portraitist of leading Scottish families, Catholic and Jacobean in particular. His support of the Jacobite cause obliged him to flee to Rome after the '45 Rebellion, where he painted members of the Old Pretender's family, including his son, Charles Edward Stuart. Alexander settled in London in 1754 and made frequent trips to Aberdeen. In 1763-4 he was working in the Netherlands and in 1766 he moved to America. He died in Scotland.