In what ways do gandalf and saruman differ in terms of fulfillment of their appointed roles?

Aruman the White, of Many Colours, The White Wizard, Head of the White Council, Lord of Isengard, Sharkey, The Boss also was a Wizard, or Istar, who lived in Middle-earth during the Third Age. Originally, he was the chief of the wizards and of the White Council that opposed Sauron. His extensive studies of dark magic, however, eventually led him to desire the One Ring for himself. Thinking he could ally himself with Sauron and then betray him, Saruman allied Isengard with Mordor in the War of the Ring, in which he was defeated.