Sam Wolowitz

Mr. Wolowitz is the ex-husband of Mrs. Wolowitz, the father of Howard Wolowitz, and the father-in-law of Bernadette Rostenkowski. He left his wife and his son when Howard was 11, which was mentioned in "The Precious Fragmentation",  "The Fish Guts Displacement" and "The Habitation Configuration". His whereabouts are currently unknown.

On Howard's 18th birthday, Mr. Wolowitz left him a letter which went unopened for many years until Sheldon was reorganizing Howard's closet in "The Closet Reconfiguration". Sheldon told its contents to all the members of the gang, except for Howard, who did not want to know, and burned the letter. At the end of the episode, everyone told Howard a different story; Raj said that it contained a birthday card, Amy said that Howard's dad attended his high school graduation, Leonard said it spoke of the important of family, Penny said Howard's dad had a secret life that he needed to return to, Bernadette said it was a picture of Howard being held by his dad on the day he was born, and Sheldon said it was a map to buried treasure. One of these stories is true, but exactly which one is unknown to Howard and the viewers.