In addition to being a famous physicist, he's also a great novelist.
Literal
Famous-[attributive-な] physicist be-[nominal-こと]-[in-addition-に加えて], he [topic-は] great-[attributive-な] novelist [also-でも] be.
~に加えて ('in addition to') is a formal additive connector that requires nominalization with こと when attaching to a clause: '~ことに加えて' = 'in addition to the fact that ~.' Compared with the related ~上に, ~に加えて is even more formal and writerly, common in essays, news, and biographical prose.