I know I often say this but I have genuinely never, ever heard of him.
I've just looked him up on IMDb and I understand why. Not only have I not heard of him, but, apart from The Madness of King George (which I have seen but I've no idea what part Sir Ian played) I haven't heard of much that he has been in either. I've heard of "Little Red Riding Hood" and "Alice Through the Looking Glass" but stories, not films. I've heard of "Lord of the Rings" (I read about three pages of the book - puerile drivel) and Chariots of Fire but that's about it.