Who is Robert Cecil from The Last Lion: Winston Spencer Churchill and what is their importance?

Robert Cecil, Marquess of Salisbury is a British Prime Minister at the time of the Irish Home Rule issue. He knows Randolph Churchill wants his job so he appoints him as Chancellor of the Exchequer and waits for him to fail, which he does. The conservatives and Salisbury are rejected in summer of 1892. He is still the Prime Minister when Winston is elected.