“The Big Bang Theory” doesn’t often devote itself to the subplot of Howard’s past life. If that’s the case, there’s a lot of sensitivity as to where Howard’s father Sam ended up.
Throughout the show, it is slowly revealed why Howard’s mother was a single parent. In The Precious Fragmentation, viewers learn that Sam started the family when Howard was 11 years old. It’s a “blink and you’ll miss it” moment as the group opens a box they bought at the flea market and Howard finds an ALF doll like the one his mother bought for him immediately after his father neglected him got.
The reason Sam left is not explored until Season 6 Episode 19. Here Sheldon stumbles across a letter that his father sent Howard for his 18th birthday. It includes Sam’s explanation for leaving his wife and son behind, but viewers – and Howard – are still not sure why. As? Well, Howard explains that he both wants to know and doesn’t want to know what the letter says, so the gang’s solution is to give Howard several false explanations and one true explanation without telling him which is which. It seems to offer enough closure to let the subject rest for a few seasons.
Finally, in Season 8 Episode 20, “The Fortification Implementation,” it is revealed that Howard has a half-brother, Josh (Matt Bennett), who explains that Sam had a different family in the years after he left Debbie and Howard .