He was born in Denver, Colorado, in 1906, the son of Jewish immigrants. He was born at a weight of less than four pounds. Jacob was small for his age, until he reached his seventh birthday. By the time was ten, he was over six feet tall. His family lived in El Paso Texas at this time and the locals nicknamed him "Pecos Bill" (a title he used for over twenty years.) Because of his intimidating height, he would avoid people by walking the alleys on his way to school so he could hide if he encountered anyone (for fear of frightening them).