Below are rules to show you how to use subject pronouns.
Subject pronouns are followed by the to be verb:
There is no subject for the infinitive to be.
For this reason, we would use the subject pronoun (he).
To make the sentence less awkward, you could rewrite it as:
It seems to be Harold who is winning the contest.
Subject pronouns are used to replace a proper noun in a sentence.
Bob waved at the girl.
He waved at the girl.
He is replacing the proper noun Bob.
It was she who called.
She was the one who called.
It was they who came to dinner last night.
They are the ones who came to dinner last night.
Below is the sentence without a subject:
Harold seems to be he who is winning the contest.
If the infinitive to be does not have a subject, use the subject pronoun that agrees with the subject of the sentence.
Keep in mind: Harold is the subject. However, Harold is not the subject of the infinitive to be.
Harold is the subject of the linking verb seems.
Below is the sentence with a subject:
His fans considered the favorite television actor to be him.
The subject of the infinitive to be is actor.
To make the sentence less awkward, you could rewrite it as:
His fans considered him to be the favorite television actor.
His fans is the complete subject and considered is the verb.
You will be able to tell where the subject and verb are as well as where the to be infinitive is located.
When the sentence is written as shown above, the object pronoun him will come before the to be infinitive.
Infinitive Without a Subject
Infinitive With a Subject
If the infinitive to be does have a subject, use the subject pronoun that agrees with the subject of the sentence.
Language Arts: Subject Pronouns