Was Jesus Christ invented? As opposed to being a sort-of god or angel who became reinterpreted as having a human existence. That god-to-human theory is advocated by Earl Doherty [jesuspuzzle.com] and Richard Carrier [richardcarrier.info] - "On the Historicity of Jesus"
The two main invention theories that I know of are the Flavian-emperor theory and the Constantine theory.
The first one is proposed by Joseph Atwill in "Caesar's Messiah" [caesarsmessiah.com] - JC was invented by members of the Flavian dynasty of Roman emperors (Vespasian, Titus, Domitian) and associates like Josephus around 80 CE.
The second one is proposed by a certain "Mountainman" [mountainman.com.au] - JC was invented by Roman Emperor Constantine and his associates early in the 4th century CE.
Both theories I consider very implausible, especially the Constantine one.