|Artistic Cartesian coordinate rendition of a singularity formed inside of a black hole.|
The term singularity was introduced in the 1960s and 1970s works John Wheeler, coiner of the term “black hole”, Subrahmanyan Chandrasekhar, Rodger Penrose, and Stephen Hawking. In 1976, in relativistic thermodynamics, the term “Schwarzchild singularity” was being used, referring to the Schwarzchild radius corresponding to the formation of a singularity. 
In 1920, American thinker William Sidis posited that the universe may have started in a “big collision”. 
In 1943, English thermodynamicist Alfred Ubbelohde posited that, just as there is a lower limit to temperature (third law) there may be an upper limit to temperature, such that at sufficiently high temperatures, all matter may resolve into radiation, and that this upper limit of temperature may be related to some kind of thermodynamic ‘starting-point’ of the universe. 
In the 1973 book The Large Scale Structure of Space-Time (and followup 1986 A Brief History of Time), Stephen Hawking seems to have introduced the view that the universe originated as a “initial singularity” some 10 to 15 billion years ago. 
Depending on argument, some have posited that the so-called initial singularity of the universe started in either a state of low entropy or of high entropy.
In the mid 20th century, religious theorizers began to argue that the singularity was god, created by god, or the power or force of god, or something to this effect. An example is found in the work of British astrophysicist Edward Milne, published between 1933 and 1950, who argues that owing to the creative power of god, the universe must have started in a point-singularity; Milne also discussed this theory in the context of Rudolf Clausius' end state heat death theory, which he seems to have objected to. 
1. Daintith, John. (2005). Oxford Dictionary of Science. Oxford University Press.
2. Weiss, Richard A. (1976). Relativistic Thermodynamics, Volume 2 (pg. 123). Exposition Press.
3. Kragh, Helge S. (2008). Entropic Creation: Religious Contexts of Thermodynamics and Cosmology (singularity, pg. 198). Ashgate Publishing, Ltd.
4. Sidis, William J. (1920). The Animate and the Inanimate, [PDF], (published in 1925, R.G. Badger).
5. Ubbelohde, Alfred René. (1947). Time and Thermodynamics (pg. 25). Oxford University Press.
6. Ellis, G.F.R. and Hawking, Stephen W. (1973). The Large Scale Structure of Space-Time (singularity, 83+ pgs). Publisher.
● Gravitational singularity – Wikipedia.
● Penrose-Hawking singularity theorems – Wikipedia.