Tysha was Tyrion Lannister’s first wife, but her story was omitted from the Game of Thrones television series. In the books, Tyrion meets Tysha, a young crofter’s daughter, after defending her from attackers. The two quickly fall in love and secretly marry, believing their relationship to be genuine.
Tywin Lannister discovers the marriage and claims Tysha was merely a prostitute hired by Jaime to initiate Tyrion sexually. Tywin then forces Tyrion to watch his guards abuse Tysha, before making Tyrion participate. Tyrion is told that the marriage has been annulled, and he carries that trauma for years.
The truth is revealed much later: Tysha was not a prostitute, and Jaime had lied because Tywin ordered him to conceal the marriage. This revelation profoundly affects Tyrion’s actions after his trial. The television series retained Tyrion’s later marriage to Sansa Stark and his relationship with Shae, but removed Tysha and the revelation about her entirely.
A common mix-up is treating Shae as Tyrion’s first wife. Shae was his lover in both versions, while Sansa was his second wife in the novels; their marriage was never consummated.