"The Big Bang Theory" is an American comedy television series created and executively produced by Chuck Lorre and Bill Prady.
 Like the name of the series itself (with the exception of the first episode "Pilot"), episode titles of "The Big Bang Theory" always start with ""The"" and resemble the name of a scientific principle, theory or experiment, whimsically referencing a plot point or quirk that is stated in that episode.
Physical cosmology is the study of the largest-scale structures and dynamics of the Universe and is concerned with fundamental questions about its origin, structure, evolution, and ultimate fate.
 Cosmology as a science originated with the Copernican principle, which implies that celestial bodies obey identical physical laws to those on Earth, and Newtonian mechanics, which first allowed us to understand those physical laws.
 Physical cosmology, as it is now understood, began with the development in 1915 of Albert Einstein's general theory of relativity, followed by major observational discoveries in the 1920s: first, Edwin Hubble discovered that the universe contains a huge number of external galaxies beyond our own Milky Way; then, work by Vesto Slipher and others showed that the universe is expanding.
 These advances made it possible to speculate about the origin of the universe, and allowed the establishment of the Big Bang Theory, by Georges Lemaitre, as the leading cosmological model.
 A few researchers still advocate a handful of alternative cosmologies; however, most cosmologists agree that the Big Bang theory explains the observations better.
Kevin Sussman (born December 4, 1970) is an American actor.
 He is known for playing Stuart Bloom on the CBS sitcom "The Big Bang Theory" and Walter on the ABC comedy-drama "Ugly Betty".
 Starting with the sixth season of "The Big Bang Theory", he was promoted to a series regular.
Sheldon Lee Cooper, Ph.D., Sc.D.
, is a fictional character in the CBS television series "The Big Bang Theory" and "Young Sheldon", portrayed by actor Jim Parsons in "The Big Bang Theory" and Iain Armitage in "Young Sheldon".
 For his portrayal, Parsons has won four Primetime Emmy Awards, a Golden Globe Award, a TCA Award, and two Critics' Choice Television Awards.
 The childhood of the character is the focus of "Young Sheldon", the show being set in 1989, when 9-year-old Sheldon, who has skipped ahead four grades, starts high school alongside his older brother.
The first season of the American sitcom "The Big Bang Theory" was originally aired on CBS from September 24, 2007, to May 19, 2008, over 17 episodes.
 An unaired pilot also exists.
 The Season 1 DVD came without a gag reel and is, so far, the only "Big Bang Theory" DVD set not to have one.
 The reissued Blu-ray, was released July 10, 2012, and includes a gag reel that is exclusive to the set.
 The episodes on Blu-ray are all in remastered surround sound, whereas the DVD version had stereo.
 Two of the main cast, Sheldon and Leonard, are named after actor, director, and producer Sheldon Leonard.
John Mark Galecki (born April 30, 1975) is an American actor.
 He is known for playing David Healy in the ABC sitcom "Roseanne" from 1992 to 1997 and Dr. Leonard Hofstadter in the CBS sitcom "The Big Bang Theory" since 2007.
 Galecki also appeared in the films "National Lampoon's Christmas Vacation" (1989), "Prancer" (1989), "Suicide Kings" (1997), "I Know What You Did Last Summer" (1997), "Bookies" (2003), and "In Time" (2011).
Since the emergence of the Big Bang theory as the dominant physical cosmological paradigm, there have been a variety of reactions by religious groups regarding its implications for religious cosmologies.
 Some accept the scientific evidence at face value, some seek to harmonize the Big Bang with their religious tenets, and some reject or ignore the evidence for the Big Bang theory.
Young Sheldon (stylized as young Sheldon) is an American television sitcom on CBS created by Chuck Lorre and Steven Molaro.
 The series is a spin-off prequel to "The Big Bang Theory" and follows the character Sheldon Cooper at the age of 9, living with his family in East Texas and going to high school.
 Iain Armitage stars as young Sheldon, alongside Zoe Perry, Lance Barber, Montana Jordan, and Raegan Revord.
 Jim Parsons, who portrays an adult Sheldon Cooper on "The Big Bang Theory", narrates the series and serves as an executive producer.
Rings is a 2017 American supernatural psychological horror film directed by F. Javier Gutiérrez, written by David Loucka, Jacob Aaron Estes and Akiva Goldsman and starring Matilda Lutz, Alex Roe, Johnny Galecki, Aimee Teegarden, Bonnie Morgan and Vincent D'Onofrio.
 It is the third film in "The Ring" series.
 The film takes place thirteen years after the events of the 2002 film.
In cosmology, recombination refers to the epoch at which charged electrons and protons first became bound to form electrically neutral hydrogen atoms. Recombination occurred about 378,000 years after the Big Bang (at a redshift of "z" =  ).
 The word "recombination" is misleading, since the big bang theory doesn't posit that protons and electrons had been combined before, but the name exists for historical reasons since it was named before the Big Bang hypothesis became the primary theory of the creation of the universe.

Question: Who is the actor in "Rings", "Roseanne", and "The Big Bang Theory"?
Answer: Johnny Galecki