His will is strong as an oak.
When like or as are used to compare something, it is a simile.
If the comparison had been actually applied to the person, it would have been a metaphor. Example: "Wyatt, you're an oak."
With metaphors the comparison is not as direct.
He thundered around the house.
A metaphor
A metaphor, a simile uses the words like or as.
simile
that man
simile
steel an ox metal a teak tree a bear an oak tree
simile
simile and METAPHOR AND PERSONIFICATION AND CHEESE
simile
simile
Its a metaphor
As quick as a wink is a simile. ----