Short answers, pulled from the story.
King Cymbine is based on Cunobeline, a real British ruler mentioned by Suetonius in his Life of Caligula. This historical figure also appears in Orosius's Historia adversus Paganos and holds a significant place in Medieval Welsh literature under names like Cynfelyn or Kymbelinus.
The subplot involving Posthumus and Iachimo's wager comes directly from Giovanni Boccaccio's The Decameron, specifically story II.9. Another influence was the anonymously authored Frederyke of Jennen, which shares similar characters and wager terms with Shakespeare's narrative. A third inspiration was a play called The Rare Triumphs of Love and Fortune, first performed in 1582, featuring parallels to the lost princes storyline.
Although listed as a tragedy in the First Folio published in 1623, modern critics often classify Cymbeline as a romance or even a comedy. Samuel Johnson took issue with its complex plot during the eighteenth century when the play was one of Shakespeare's more popular works while William Hazlitt and John Keats numbered it among their favourite plays despite its difficulties.
After the 1611 performance mentioned by Simon Forman there is no record of production until 1634 when the play was revived at court for Charles I and Henrietta Maria noted as well likte by the kinge. In 1728 John Rich staged the play with emphasis placed on spectacle rather than text.
Lucius J. Henderson directed the first screen adaptation in 1913 produced by Thanhouser Company starring Florence La Badie James Cruze and William Garwood. Beethoven's opera Fidelio references Imogen's cross-dressing as Fidele through loyal wife Leonore disguising herself as a man while Elijah Moshinsky directed BBC Television Shakespeare adaptation in 1982 ignoring ancient British period for timeless snow-laden atmosphere inspired by Rembrandt.