彼はいわば歩く百科事典だ。
tbd
He's what they call a walking encyclopedia.
He is, so to speak, a walking encyclopedia.
は
1. indicates sentence topic
2. indicates contrast with another option (stated or unstated)
3. adds emphasis
指示句子的主题;表示与另一选项(无论是否明确提及)形成对比;表示强调