Can I say
Why should I be the first who call him?
Or should I say
Why should I be the first to call him?
in present tense, referring to the future?
English Language Learners Stack Exchange is a question and answer site for speakers of other languages learning English. It only takes a minute to sign up.Sign up to join this community
Either is acceptable, but the version with the infinitival clause (first to call) is far more common.
Note that if you do use the version with the relative clause, the verb call must be in the third person and agree with the referent of who in number:
I will be the first [person] who calls him.
We will the first [people] who call him.
Use a non-finite clause when the subject is the same as the subject in the main clause. We can understand the time/tense referred to from the context of the main clause. we often use "to-infinite" in non-finite relative clause after ordinal numbers (the first, the second etc.), superlatives (the best, the most beautiful etc.) and after next, last and only.
So, Why should I be the first to call him? is correct.