The American spymaster是主语,
who built the Office of Strategic Services in World War 2 and later
laid the roots for the CIA 是定语从句,修饰限制The American
spymaster.
was fascinated with minformation.是谓语部分。
你没搞清楚什么是主语从句。主语从句是指一个名词性的句子放在主语的位
置上充当主语,而本句中已经有The American spymaster做主语,who后面的
只能是定语从句。