Whoever and Whomever

Rule 1

First of all, use the ever suffix when who or whom can fit into two clauses in the sentence.

Whoever/whomever Example

Give it to whoever/whomever asks for it first.
Give it to him. He asks for it first.

Rule 2

Because we can substitute him and he in both clauses, we must use the ever suffix. Now, to determine whether to use whoever or whomever, here is the rule:

him + he = whoever
him + him = whomever
Therefore, Give it to whoever asks for it first.
Examples We will hire whoever/whomever you recommend.
We will hire him. You recommend him.
him + him = whomever
We will hire whoever/whomever is most qualified.
We will hire him. He is most qualified.
him + he = whoever

Rule 3

When the entire whoever/whomever clause is the subject of the verb following the clause, look inside the clause to determine whether to use whoever or whomever.
Examples

Whoever is elected will serve a four-year term.

Whoever is elected is the subject of will serve.

Whoever is the subject of is.

Whomever you elect will serve a four-year term.

Whomever you elect is the subject of will serve.

Whomever is the object of you elect.