Christ myth (image)
Left: The image (Ѻ) of the 1st dynasty pharaoh Hor-Aha (c.3050), i.e. “pharaoh Aha god Horus incarnate”, standing over or holding some type of Ankh (life symbol) figure. Right: image of Jesus on the Ankh, from the cover of Timothy Freke and Peter Gandy’s Jesus and the Lost Goddess. Jesus, according to Christ myth theory, is a morph of aspects of the Egyptian mythological gods: Ra, the sun god, the main god of Heliopolis, Osiris, the afterlife god, the nome god of Busiris, and Horus, one of the most ancient gods of Egypt, originally worshipped in three nomes of of Upper Egypt and two nomes of lower Egypt.
In mythology, Christ myth theory, an early 20th century term, aka Christ fable (Leo X, 1514), “Christ fairytale” (Goethe, 1810), Jesus myth (Peebles, 1870), “Christian mythology” (Haeckel, 1899), Christ myth (Drews, 1909), refers to the conjecture that Jesus Christ never existed, but is but a mythological figure; an Osiris-Horus-Ra morph or god syncretism to be specific, predominately speaking.

Overview
In 2000, Robert Price, in his Deconstructing Jesus (pg. 17), summarized things as follows:

“Generations of Rationalists and freethinkers have held that Jesus Christ corresponds to no historical character: There never was a Jesus of Nazareth. We might call this categorical denial ‘Jesus atheism’ [see: achristism] What I am describing is something different, a ‘Jesus agnosticism’. There may have been a Jesus on earth in the past, but the state of the evidence is so ambiguous that we can never be sure what this figure was like or, indeed, whether there was such a person.”

In 2006, Peter Joseph published the viral documentary Zeitgeist which introduced the then-undergound field of Christ myth research, e.g. Gerald Massey, Dorothy Murdock, Jordan Maxwell, etc., to the general public, after which the term "Zeitgeist" became a cultural meme as code for loose knowledge that Jesus as a religious figure is but allegory of an older parallel religio-mythology story.

Quotes
The following are noted quotes:

Jesus, Moses, and Muhammad are imposters.”
Frederick II (c.1235), Treatise on the Three Imposters

“How well we know what a profitable superstition this fable of Christ has been for us and our predecessors.”
Pope Leo X (1514), toast during Good Friday banquet, Vatican

Christianity is the fairytale of Christ. Jesus Christ is not the author of Christianity, but rather it is a subject composed by a number of wise men. Christian religion is merely a rational, political institution.”
Johann Goethe (1770/1810), law school dissertation + later quote (see: Goethe on religion) [2]

“It is also extremely difficult to ascertain whether those books belong to the authors whose names they bear. In the first ages of Christianity there was a great number of gospels, different from one another, and composed for the use of different churches and different sects of Christians. The truth of this has been confessed by ecclesiastical historians of the greatest credit. (Tillemont, tom. ii. 47, etc. Epiphan. Homil. 84. Dodwell's Disser. on Irenaeus, p. 66. Freret's Examin. Critique. Codex Apocryphus, &c.) There is, therefore, reason to suspect, that the persons who composed the acknowledged gospels might, with the view of giving them more weight, have attributed them to apostles, or disciples, who actually had no share in them. That idea, once adopted by ignorant and credulous christians, might be transmitted from age to age, and pass at last for certainty, in times when it was no longer possible to ascertain the authors or the facts related. Among some fifty gospels, with which Christianity in its commencement was inundated, the church, assembled in council at Nice [325AD], chose four of them, and rejected the rest as apocryphal, although the latter had nothing more ridiculous in them than those which were admitted. Thus, at the end of three centuries, (i.e. in the three hundred and twenty-fifth year of the Christian era,) some bishops decided, that these four gospels were the only ones which ought to be adopted, or which had been inspired by the Holy Spirit. A miracle enabled them to discover this important truth, so difficult to be discerned at a time even then not very remote from that of the apostles.”
Baron d’Holbach (1770), Critical History of Jesus Christ (pgs. 10-11)

“The second treatise, entirely devoted to the examination of the religious system of the Christians, is also divided into three parts. The first contains the explanation of the sacred fable of the introduction of evil into the world by the famous Serpent of the Hesperides, which seduced Eve, and which necessitated the arrival of a Repairer, who could regenerate Nature. Is found in the second chapter of the Hebrew Cosmogony, known as the Genesis. The second deals with Repairer, of his birth, of his death, and of his resurrection; it presents us with all the features which are common to it with: Mithra, Adonis, Horus, Atys, Osiris, etc. And finally, which prove up to the dawn of time, that this designated Repairer, named the Christ by the Christians, is only the sun, or the divinity endured by all peoples, under so many different forms and names. The third part, much more abstract than the first two, contains an explanation of the famous Triad of the Christians, or the triple unity, known under the names of Father, Son, and Holy Spirit.”
Charles Dupuis (1771), “Article” in Journal of Savants; refined version as found in preface of volume one (pg. xxviii) of his 12-volume Universal Religion (1794)

Christ is etymologically related to Bacchus and Christna [Krishna], i.e. sun god worship beliefs; Abraham and his wife Sarah are etymologically related to Brahma and his wife Saraswati; the god of Moses was Egyptian.”
Constantin Volney (1791), The Ruins; paraphrase of Joseph Priestley (1797) and Nigel Leask (2004)

“The Christian religion and Masonry have one and the same common origin: both are derived from the worship of the Sun. The difference between their origin is, that the Christian religion is a parody on the worship of the Sun, in which they put a man whom they call Christ, in the place of the Sun, and pay him the same adoration which was originally paid to the Sun.”
Thomas Paine (c.1804), “Essay on the Origin of Free-Masonry”

“I have dictated thirty pages on the world’s three religions; and I have read the Bible. My own mind is made up. I do not think Jesus Christ ever existed.”
Napoleon Bonaparte (1817), “Dialogue with Gaspard Gourgaud”, Apr

Jesus Christ in the New Testament, has no reference whatever to any event that ever did in reality take place upon this globe; or to any personages that ever in truth existed: and that the whole is an astronomical allegory, or parable, having invariably a primary and sacred allusion to the sun, and his passage through the signs of the zodiac; or a verbal representation of the phenomena of the solar year and seasons.”
Logan Mitchell (1842), Christian Mythology Unveiled

“There are few points on which the Egyptian and Christians religions so nearly analogize, and which are more striking in their resemblances than that one doctrine which has always been regarded, and rightly so, as a special result of revelation, —the doctrine of a ‘vicarious deliverer’ of mankind in the person of a mysterious Being, who is at once both very god and very man. The definite language of the Nicene Creed, and its commentary, the symbol of St. Athanasius, explains the nature and attributes of the founder of our religion, and it is my province, as far as I am able to do so, to show to-night in what degree that nature and those attributes were anticipated in the Egyptian dogma of Horus Nets, the only-begotten son of his father—the ‘deliverer of mankind’ from the ‘evil one’.”
William Cooper (1877), The Horus Myth in its Relation to Christianity

Christianity was not invented by the fathers of the church. It was all taken in a ready-made form from Egypt, only not from the Egypt that we know but from one which we do not know. This Egypt was in the same place as the other but it existed much earlier ... prehistoric Egypt was Christian many thousands of years before the birth of Christ.”
George Gurdjieff (c.1915), reported (Ѻ) by P.D. Ouspensky; cited by Simson Najovits (2009)

“Historically, it is quite doubtful whether Christ ever existed at all, and if He did we do not know anything about Him, so that I am not concerned with the historical question, which is a very difficult one.”
Bertrand Russell (1927), “Why I Am Not a Christian” (Ѻ)

“The Christian myth of the 'return' is a powerful allegory designed to guide us through the stages of initiation which lead to Gnosis. It was created by synthesizing the Jewish myth of Exodus with Pagan myths of the dying and resurrecting Godman Osiris-Dionysus. Originally a simple and abstract myth, it was revised and embellished over the course of the first and second centuries CE to become the most influential myth ever created: the Jesus story.”
Timothy Freke and Peter Gandy (2001), Jesus and the Lost Goddess [1]

“Since The Christ Conspiracy [Dorothy Murdock, 1999] perfectly explains how Christianity is astrotheology, and Jesus and the Lost Goddess [Timothy Freke and Peter Gandy, 2001] explains how Christianity is Gnosticism and explains much of the religio-philosophy of Gnosticism, why should I bother buying and reading books about the history of established Christianity -- why bother studying the history of folly? It's remarkable how little the Christ-myth scholars and entheogen scholars are aware of each other. It shouldn't take long to introduce them to each other, Yes the Christ-myth theory (that Jesus is mythic/mystic and not historical) is greatly helpful in overall understanding of Christianity.”
— Michael Hoffman (2004), “Studying Mainstream vs Proto-Christianity” (Ѻ)(Ѻ)

“The truth is that Christianity grew from neither a god nor a man, but out of what had gone before. A ‘human Jesus’ was no more necessary than was a human Horus, a human Dionysus, or a human Mithras.”
— Kenneth Humphreys (2005), Jesus Never Existed (pg. 21)

References
1. Freke, Timothy and Grandy, Peter. (2001). Jesus and the Lost Goddess: The Secret Teachings of the Original Christians (Osiris, 18+ pgs; quote, pg. 13). Random House.
2. (a) Fink, Karl J. (2009). Goethe’s History of Science (pg. 9; physical sciences, pgs. 75-76). Cambridge University Press.
(b) Haught, James A. (1996). 2000 Years of Disbelief: Famous People with the Courage to Doubt (§: Johann Goethe, pgs. 105-07). Prometheus.

Further reading
● Peebles, James M. (1870). Jesus: Myth, Man, or God – the Popular Theology and the Positive Religion Contrasted. J. Burns.
● Smith, William B. (1894). Ecce Deus: The Pre-Christian Jesus (Ѻ) . Publisher.
● Drews, Arthur. (1909). The Christ Myth (Die Christusmythe)). Prometheus, 1911.
● Robertson, Archibald. (1946). Jesus: Myth or History? (Arc) Watts & Co.
● Kryvelev, Iosif A. (1987). Christ: Myth or Reality? Social Sciences Today.
● Humphreys, Kenneth. (2005). Jesus Never Existed (abs). Iconoclast Press.
● Doherty, Earl. (2009). Jesus: Neither God Nor Man - The Case for a Mythical Jesus. Age of Reason Publications.

External links
Christ myth theory – Wikipedia.
Christ myth theory – WikiQuote.
Jesus myth theory – RationalWiki.

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