Leonard and Michael's Grandfather

This man was the father of either Dr. Hofstadter or Beverly Hofstadter and the grandmother of Leonard Hofstadter, Michael Hofstadter and Hayley Hofstadter.

On one of Leonard's birthdays, Leonard came home from his cello lesson to find lots of strange cars parked out front and when he got to the door, he could hear people whispering and he could smell German chocolate cake which was his favourite, but it turned out his grandfather had died. Leonard said it felt a bit like a birthday party because he got to see his cousins and there was cake.