Man of Steel. Man in Blue. The Big Boy Scout. These are all nicknames used for Superman.

When using the phrase 'man of steel', for example, in a sentence, when should it be capitalized "Man of Steel" and when should it be left lowercase "man of steel"? Are some nicknames more likely to be capitalized than others?

This is one of those blurry line issues I'm never sure on.

What do you think?

VirginiaR.
"On the long road, take small steps." -- Jor-el, "The Foundling"
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"clearly there is a lack of understanding between those two... he speaks Lunkheadanian and she Stubbornanian" -- chelo.