Sir Thomas de Ashton or Assheton (fl. 1446), was an English alchemist. Ashton was born in 1403, the son and heir of Sir John de Ashton, of Ashton-under-Lyne, who died in 1428. His half-brother Ralph de Ashton seems to have inherited the main family home, Ashton Hall. From roughly this date, differences appear in the coat of arms, motto and spelling of the two families, indicating that Sir Thomas may have distanced himself from his unpopular half-brother.