The correct option is
C Was
The given sentence is in past tense, it describes events that have already happened. We can conclude this from the given words "was born...was interested...was working...", which expresses the past tense.Option C: 'Was' is a past tense verb and expresses a past event in the sentence 'his name was Erich'. Hence option C is correct.
Option A: 'Is' refers to the simple present tense and we use it to refer to a fact that is still true. But, the person 'he' has changed his name now and isn't 'Erich' anymore. So 'is' is not the appropriate option here.
Option B: 'Had been' expresses the past perfect tense. We use the past perfect to refer to an action that completed before another action started. Since there is only one action here, the sentence is not in past perfect.
Option D: 'Were' is a past tense verb in plural form. The verb must agree with the subject in terms of number. Since the subject 'His name' is singular, the verb must also be singular.
Hence these options are wrong.