I don’t know if iconic is the right term, but James McAvoy really lands the big famous roles from famous books and comics. Here is a list of roles he has played.
Mr. Tumnus – Narnia <-Famous series, probably pushing it to call the role iconic
Leto II – Dune
Professor X – X-men
Lord Asriel – His Dark Materials
Dream(Morpheus) – The Sandman(audio)
Dream was only in the audible version of Sandman, but getting to play Leto II, Professor X, and Lord Asriel is kind of a lot for one actor.
To be fair, he is very good. But he really has some connections or something.
They’re all in very similar genres, almost a niche market, so it wouldn’t be surprising if producers and directors of something similar thought of him.
And of course his Glaswegian air-traffic controller bit on SNL. But the most impressive thing of his I’ve seen is the young fictitious doctor co-starring with Forrest Whitaker’s amazing (and Oscar-winning) Idi Amin in The Last King of Scotland.