Robert Jacobs is an Associate Justice of the Supreme Court of the United States. A close friend of Solicitor General Heather Dunbar. He is diagnosed with Alzheimer's two months before the start of Season 3.
Justice Jacobs served on the Supreme Court for 23 years before the events of Season 3, so would have been appointed in 1993 by President Bill Clinton. He is known as the 'swing vote' in many Supreme Court decisions.
Two months prior to the start of Season 3, Jacobs was diagnosed with Alzheimer's. Despite the disease not affecting his judgement on the bench, Jacobs requests that President Frank Underwood allows him to retire before symptoms become apparent. Both Underwood and Vice President Donald Blythe convince him to remain on the court until the America Works program is put into action, as it would be difficult to also deal with a Supreme Court nomination. Underwood also believes Republican opposition would push the legislation towards the Supreme Court, and would rely on Jacobs support.
Later in Season 3, Jacob's conditions worsens. Underwood then pledges, that he makes the decision to retire and asks Heather Dunbar to take his place. Dunbar at first made a surprised impression and accept the post, but later its known, that she know Jacobs very well and knew about his Alzheimer's since the diagnosis.