According to the Arthurian Circle legends, Guinevere was the wife of King Arthur, daughter of King Leondegrance and had a secret affair with Arthur's greatest knight Lancelot. She is one of the most iconic characters of Arthur's legend, as she is bound to appear in several adaptations and is believed her forbidden romance with Lancelot is to have caused the kingdom's downfall.
In Other Media
Guinevere was portrayed by British actress Angel Coulby. She appeared throughout all 5 seasons of the the British show.
She started as a lowly servant of Morgana Le Fey and throughout the seasons she rose in ranking and eventually married King Arthur and became Queen.