The adjective opportunist means someone who takes advantage of any situation to gain money or power, without considering whether their actions are right or wrong.

Synonyms are go-getter, ingrate, bounder, or carpetbagger.

The word origins from late 19th century. It comes from the English opportune meaning “well-chose” plus ist.

This is clearly a work of an opportunist thief.

They haven’t thought he has opportunist goals.

She’s a ruthless political opportunist.