Professors, scientists, lab technicians and students, but not medical personnel that appear in various episodes.
Analeigh Tipton as Vanessa in The Mystery Date Observation a beautiful girl that was interested in physics, flags, and Klingon who answered Sheldon's dating ad.
Tom Fonss as Student in The Romance Resonance who cheers Sheldon in the Caltech cafeteria.
Todd Eric Andrews as Dr. Gunderson in The Workplace Proximity who was Amy's Swedish colleague that Sheldon insulted.
Ayumi Iizuka as Scientist in The Workplace Proximity who was one of Amy's colleagues at Caltech.
Sophie Oda as Grace in The Hofstadter Insufficiency who was a colleague on the boat during Leonard's North sea expedition.
Aaron Takahashi as Scientist in The Hofstadter Insufficiency who was a colleague on the boat during Leonar]'s North sea expedition.
Julie Michaels as Professor in The Prestidigitation Approximation.
William Ngo as Chinese Grad Student in The Tangerine Factor who was the Chinese graduate student confused by Sheldon's pidgin Chinese.
Paul Willson as Professor Sharpe in The Champagne Reflection as Professor Roger Abbott's former office roommate.
Lynn Philip Seibel as Professor Rothman in The Rothman Disintegration as the looney retiring professor.
Peter MacNicol as Doctor Wolcott in in The Reclusive Potential as a reclusive physics genius who lives in the woods.
Melissa Tang as Mandy Chow in The Separation Oscillation as the girl that Leonard kissed on his North Sea expedition.
Rick Fox as Glenn in The Love Car Displacement as Bernadette's old professor and former boyfriend.
Adam Gregor as Dimitri in The Bat Jar Conjecture as Caltech janitor that used to be a professor in the former Soviet Union.
Ryan Cartwright as Cole in The 43 Peculiarity as Penny's classmate.
Oliver Muirhead as Professor Laughlin in The Pirate Solution as a professor interested in working with Raj.
Austin Lee as Dennis Kim in The Jerusalem Duality as a rival to Sheldon from North Korea.
Daniel Levitin as Professor in Cafeteria in The Focus Attenuation.
Judy Greer as Dr. Plimpton in The Plimpton Stimulation as Sheldon's oversexed academic guest.
Elizabeth Bogush as Dr. Catherine Millstone in The Pirate Solution as a prospective female colleague of Raj's who he propositions.
Lewis Black as Professor Crawley in The Jiminy Conjecture as a Caltech bug expert.
Michael Trucco as Dr. David Underhill in The Bath Item Gift Hypothesis as a brilliant physicist that Penny dates.
D.J. Qualls as Toby Loobenfeld in The Loobenfeld Decay as a Caltech technician/amateur actor.
Robert Clotworthy as Headmaster in The Graduation Transmission of Leonard's old high school.
Joel Brooks as Professor Goldfarb in The Jerusalem Duality as Professor that Sheldon discusses his New Jerusalem project in Mexico with.
Chris Smith as Matt in The Tangible Affection Proof as the man who proposes to Gretchen and was Penny's old boyfriend.
Jen Drohan as Martha The Psychic Vortex as the graduate student who likes Green Lantern and Sheldon.
George Wyner as Dr. Zhang The Proposal Proposal who was a colleague who praised Amy during a dinner with Sheldon in Princeton NJ.
Susan Chuang as Dr. Harris The Proposal Proposal who was a colleague who praised Amy during a dinner with Sheldon in Princeton NJ.
Eddie Shin as Dr. Park in The Planetarium Collision who was taking over Amy's project after Sheldon asked President Siebert to have her available full-time to work on their Super-Asymmetry project.
Martin Alison Martin as Andrea in The Planetarium Collision who ran the Griffith Planetarium and was Raj's supervisor.
Hermie Castillo as Colin in The Planetarium Collision who was a grad student being tested by Amy for his sensory reactions.
David Theune as Dr. Graybel in The Imitation Perturbation.
Maribeth Monroe as Doctor Lee in The Grant Allocation Derivation as the woman who worked with crows and was looking for funding from Leonard.
David Theune as Dr. Graybel in The Decision Reverberation as a colleague at Caltech who kidded him about the news story that he had discovered evidence of alien life.