Short answers, pulled from the story.
Mark Smeaton was a court musician born to a carpenter and a seamstress who rose from humble origins to serve King Henry VIII. He worked as a singer, lute player, and dancer but remained an outsider to the Queen's inner circle due to his low social standing.
Mark Smeaton was arrested on the 30th of April 1536 and taken to Thomas Cromwell's house in Stepney. The evidence against him included a reported conversation with Anne Boleyn in the round window at Winchester and his own confession obtained under duress.
Mark Smeaton confessed to being the Queen's lover after being subjected to torture with a knotted cord around his eyes at Thomas Cromwell's house. His confession was coerced and contained factual inconsistencies regarding the date he claimed to be with the Queen.
Mark Smeaton was executed by beheading on the 17th of May 1536 at Westminster Hall. He was buried in a common grave with William Brereton after expressing his guilt on the scaffold.
Queen Mary I claimed that Elizabeth was the illegitimate child of Anne Boleyn and Mark Smeaton because she believed Elizabeth resembled Smeaton. This theory gained little traction among the public who saw a clear resemblance between Elizabeth and her father Henry VIII.
Mark Smeaton has been portrayed by Gary Bond in the 1969 film Anne of the Thousand Days and by David Alpay in The Tudors. He appears in novels by Hilary Mantel and various operas and documentaries as a man manipulated into a false confession.