<Li> Pamela Adlon as Halley Wolowitz (voice only) </Li> <Li> Joshua Malina as President Siebert </Li> <Ul> <Li> Riki Lindhome as Ramona Nowitzki </Li> <Li> Ira Flatow as himself </Li> <Li> Swati Kapila as Ruchi </Li> <Li> Beth Behrs as Nell </Li> <Li> Walton Goggins as Oliver </Li> <Li> Bill Gates as himself </Li> <Li> Peter MacNicol as Dr. Robert Wolcott </Li> <Li> Neil Gaiman as himself </Li> <Li> Lauren Lapkus as Denise </Li> <Li> Jerry O'Connell as George Cooper Jr . </Li> <Li> Courtney Henggeler as Missy Cooper </Li> <Li> Teller as Mr. Fowler </Li> <Li> Kathy Bates as Mrs. Fowler </Li> <Li> Mark Hamill as himself </Li> </Ul> <Li> Riki Lindhome as Ramona Nowitzki </Li>

Who plays dr. walcott in the big bang theory