Little is known about the prophet Malachi from the Bible, including whether his name was his real name or an assumed name meaning "messenger of YWHW." He wrote the Book of Malachi from the Bible and part of the Jewish Tanakh in the last book of Neviim.
Malachi was part of the Anshei Knesset Hagedolah, which was an assembly of 120 prophets and sages who comprised the ultimate authority in Judaism in the fourth century B.C. They met in Jerusalem in the Second Temple era. Malachi was also one of the last three prophets in the prophetic era, and his book is the last book in the Christian Old Testament.
Most of the Talmud sages believe Malachi was an actual person, but there are some who believe that Malachi was a name used either by Ezra the Scribe or Mordechai from the Purim story. This is partially because Jews of the time credited the Book of Malachi to Ezra. Most scholars believed that Malachi prophesied during the Persian period, around 416 B.C.
During this time, the people of Judah experienced great disorder, and Malachi reproved them for taking strange wives, inhumane treatment of each other, divorcing their wives and not tithing.