Here's why:
* Describes a noun: It describes the quality of something or someone. For example: "He is the strongest competitor."
* Comparative form: It is the superlative form of the adjective "strong", indicating the highest degree of strength.
However, it can also function as an adverb in some cases.
For example: "He pushed strongest of all." Here, it modifies the verb "pushed" and tells us how he pushed.
It's important to consider the context to determine the correct part of speech.