Lord Hoster Tully is the head of Riverrun and the father of Catelyn Stark, Lysa Arryn, and Edmure Tully. His brother is Brynden "Blackfish" Tully. He was a fine warrior in his day, but lost his wife and was forever changed. In A Clash of Kings, Catelyn heads to his bedside, where he has become gravely ill. He dies in A Storm of Swords, leaving Edmure Tully as the heir to Riverrun. His last word is "Tansy," who Catelyn believes is some woman he has wronged. She may or may not be the same "Tansy" living in Stoney Sept.
It may also be worth noting that Tansy was a plant used in the Middle Ages to induce miscarriages. As Catelyn notes, Lysa Arryn had a miscarriage before marrying Jon Arryn and it is possible that Hoster gave her tansy to prevent her having a bastard.