I've never actually read that Tolkien book, but I knew that Olorin was from Tolkien.
I think it was in The Two Towers.
'The Grey Pilgrim?' said Frodo. 'Had he a name?'
'Mithrandir we called him in elf-fashion,' said Faramir, 'and he was content. Many are my names in many countries, he said. Mithrandir among the Elves, Tharkûn to the Dwarves; Olórin I was in my youth in the West that is forgotten, in the South Incánus, in the North Gandalf; to the East I go not.'