How do you rewrite the similie as a metaphor?

Just take out the "as ___ as".

For example: He was as quick as lightning. (don't ever use that it is a huge cliche)

to change this simile to a metaphor, take out "as ____ as" which is the "as quick as" part.

The metaphor will therefore be: He was lightning.

Metaphors tell you the exact things the person is related to.