How do I describe a "complex nature" of a character which consists of two "competing" personality traits in one sentence?

Solution 1:

You could use "paradoxical personality" -

Paradoxical

/ˌparəˈdɒksɪk(ə)l/

adjective

: seemingly absurd or self-contradictory.


Therefore -

"[Author] examines the protagonist's paradoxical personality, ... (description of the two traits)"