Right-hand man
Describes an important assistant. Suitable when describing a man, however, is sometimes used inaccurately on other gender identities.
Why it matters
Whilst not a particularly contentious term, especially when a man is accurately involved, this is an example where 'man' is used as a default gender to describe something. Unless useful to specify gender, using gender neutral phrases help set a broader welcoming tone in the language that surrounds us.
Instead try saying:
Right-hand wo/man /person
Further External Reading Link