If you ran into Stephen Tobolowsky on the street, you would not be mistaken: Yes, you've seen him before. A childhood dentist? A former geometry teacher? Your local florist? Tobolowsky is a character actor, one of the most prolific screen and stage presences of our time, having appeared in productions that range from ''Deadwood ''to ''Glee,'' from ''Mississippi Burning ''to ''Groundhog Day.'' But Stephen Tobolowsky, it turns out, is not just an actor; he is also a dazzlingly talented storyteller and writer. He has earned a devoted base of fans for his original stories, told in front of live audiences as well as in a popular podcast. Now, for the first time, he has assembled those stories here. The result is creative mitzvah, a work of art, and a narrative feat that combines biography and essay, ranging in tone from the hilarious to the introspective. To read these pages is to enter an astonishing world that, like all art, is universal yet individual, familiar yet disquieting. A dangerous world, indeed.