In The Big Bang Theory, Sheldon's father, George Cooper Sr., was portrayed as an aloof, uncaring dad who never understood his son's genius. In the show's prequel, Young Sheldon, the character of Sheldon's dad is played by actor Lance Barber and he's much more of a decent guy. He's even a football coach! Despite this, there's still one thing about Sheldon's late father that fans have yet to see addressed on the show.
It's been revealed that Sheldon's father passed away when Sheldon was 14. The manner of his death hasn't been clearly stated but it is likely that he had a heart attack since he was obese and frequently drank beer on the show.
But there's one major thing about Sheldon's dad that hasn't been mentioned in the show - that he was cheating on his wife with Brenda Sparks. This isn't a major spoiler for the show but it could explain why Sheldon is so bitter towards his dad.
A few Redditors on the site have pointed out that this is an important detail to include in Sheldon's story as it would add more complexity to his character. They also point out that Sheldon's bitterness towards his father could be a result of his autism as it is a way to cope with being unable to fully understand or relate to other people. It's a common trait among autistic individuals. It will be interesting to see if this tidbit is ever addressed on the show.