Joanna Lannister

Joanna Lannister, is an unseen character in Game of Thrones. He is deceased when the events of the series begin and is not expected to appear in the series.

Joanna was the wife of Tywin Lannister, the Head of House Lannister and the Lord of Casterly Rock. Joanna bore him the twins Jaime and Cersei. She died giving birth to Tyrion

In the books
In the Song of Ice and Fire novels, Joanna was a cousin of Tywin and already a member of House Lannister when they married. Her children and death are unchanged.