Young Sheldon is a TV series that currently airs on CBS from September 25, 2017. It is a prequel show to The Big Bang Theory.

Cast & Character Origins

Characters	From	Date	Episode
Sheldon Cooper	The Big Bang Theory	September 24, 2007	S01E01: “Pilot”
Mary Cooper	The Big Bang Theory	October 15, 2007	S01E04: “The Luminous Fish Effect”
Missy Cooper	The Big Bang Theory	May 5, 2008	S01E15: “The Pork Chop Indeterminacy”
Connie “Meemaw” Tucker	The Big Bang Theory	Feb 4, 2016	S09E14: “The Meemaw Materialization”

(Note: Sheldon’s father George and brother George Jr. were mentioned on The Big Bang Theory before Young Sheldon started, so technically they “originated” from that show. However, my goal is to track the order of onscreen character appearances and this page reflects that.)

Guest Characters

Characters	From	Date	Episode	Crossover Type
Arthur “Professor Proton” Jefferies	The Big Bang Theory	September 25, 2017	S01E01: “Pilot”	A
Arthur “Professor Proton” Jefferies	The Big Bang Theory	December 21, 2017	S01E09: “Spock, Kirk, and Testicular Hernia”	A
ALF	ALF	January 3, 2019	S02E11: “A Race of Superhumans and a Letter to Alf”	B*
Arthur “Professor Proton” Jefferies	The Big Bang Theory	January 31, 2019	S02E14: “David, Goliath, and a Yoo-Hoo from the Back”	A
Leonard Hofstadter, Penny Hofstadter, Howard Wolowitz, Raj Koothrappali	The Big Bang Theory	May 16, 2019	S02E22: “A Swedish Science Thing and the Equation for Toast”	A
Arthur “Professor Proton” Jefferies	The Big Bang Theory	December 12, 2019	S03E10: “Teenager Soup and A Little Ball of Fib”	A
Arthur “Professor Proton” Jefferies	The Big Bang Theory	April 16, 2020	S03E20: “A Baby Tooth and the Egyptian God of Knowledge”	A
Arthur “Professor Proton” Jefferies, Amy Fowler	The Big Bang Theory	November 5, 2020	S04E01: “Graduation”	A
Howard Wolowitz	The Big Bang Theory	November 18, 2021	S05E07: “An Introduction to Engineering and a Glob of Hair Gel”	A
Amy Fowler	The Big Bang Theory	March 10, 2022	S05E16: “A Suitcase Full of Cash and a Yellow Clown Car”	A

(Note: ALF’s appearance on Young Sheldon does imply that in this universe ALF is alive and not a puppet, but it is in the context of him being behind an actor behind the scenes of the sitcom ALF.

While the episode “A Swedish Science Thing and the Equation for Toast” has appearances by younger versions of the main cast of The Big Bang Theory, later episodes have adult Amy and Howard appear in the Wonder Years style narration as extra voices. )

Outgoing Crossovers

Characters	Guest On	Date	Episode	Crossover Type
George Cooper Jr.	The Big Bang Theory	May 3, 2018	S11E23: “The Sibling Realignment”	A
George Cooper Jr.	The Big Bang Theory	May 10, 2018	S11E24: “The Bow Tie Asymmetry”	A
George Cooper Jr., Tam Nguyen	The Big Bang Theory	October 11, 2018	S12E04: “The Tam Turbulence”	A
George Cooper Sr., George Cooper Jr.	The Big Bang Theory	December 6, 2018	S12E10: “The VCR Illumination”	A

(Note: The Big Bang Theory episode “The VCR Illumination” has the actors from Young Sheldon appear via an old VHS tape.)