Option C "had been" is the correct answer because it means some event began in the past, lasted for some time,then ended. This is entirely in the past.
Past Perfect is used to talk about actions that were completed before some point in the past, here, before the birth of the subject.
Option A is incorrect because Have been means something began in the past and has lasted into the present time, but in this case, the sentence is talking about the past, when 'he' was born.
Option B is clearly incorrect because 'will be' is a tense of the Future.
Option D is incorrect because 'were' is in the simple past tense and we need a verb in the past perfect tense to suit the context.