Olenna Tyrell is played by Diana Rigg. Although Olenna is a clever and shrewd character and manipulating the story in Game of Thrones. She is out manoeuvred by Cersei on many occasions. However when Lannisters attack and plundered High Gardens, Jamie offers Olenna a peaceful ending, in drinking poison. It is in Olenna’s last moments that she reveals it is her that killed King Joffrey. A brilliant scene and a storyline left unknown for many series.