generic he / singular they
The pronoun for one person whose sex is unknown or unstated.
Use they, their, and them for one person whose sex is unknown or unstated. This covers indefinite pronouns such as everyone, anybody, and each, and generic nouns such as a driver: A tenant who moves out early forfeits their deposit. Singular they takes a plural verb: The caller said they were outside. For the reflexive, use themselves: Anyone can enroll themselves online.
Generic he is outdated. It can read as leaving women out: Every resident must register his car reads as if every resident were a man. He or she is correct but cumbersome when repeated: his or her badge and his or her key. When the group is all men, his is correct: Each of the brothers signed his name.
Examples
Use Each driver logs their hours. (Their refers to one unspecified driver without assigning a sex.)
Use The applicant said they were free. (Singular they takes the plural verb were.)
Avoid Anybody can lose his key. (His is the error: generic his can read as leaving women out. Write Anybody can lose their key.)