Sheldon Dinkleberg is a neighbor of the Turner family who Mr. Turner despises. In many episodes he is seen being nice, or doing things in which he does not have a son. For instance, he has been shown buying things with money that he will need if he had a son. He even pretended to be mean to make Mr. Turner happy, seen in Operation Dinkleberg.
Mr. Dinkleberg and Mr. Turner have a rivalry due to the fact that since the Turners had a child (Timmy Turner), they are not able to afford many of the things that the Dinklebergs can such as a robotic lawnmower and a high-powered barbecue. This rivalry has expanded to involve all members of both families, not just Mr. Turner and Sheldon, although Timmy himself is mostly indifferent or annoyed by this family feud. Sheldon is currently married to Mrs. Dinkleberg, his unnamed wife.
In later seasons, Mr. Dinkleberg has been made into an exaggeratedly perfect neighbour who is nice to the Turners, overly charitable and generous, and is extremely helpful, making Mr. Turner's hatred of him appear far less rational. His role was also increased, allowing for more episodes to be able to involve him as a character rather than stay in the background, like Operation Dinkleberg and Dinklescouts.
Sheldon has gray hair and is typically seen wearing a yellow (sometimes plaid) shirt with blue jeans. In his youth, he had blonde hair.
The Dinklebergs, particularly Sheldon Dinkleberg, were introduced as Mr. Turner's enemy. Eventually this grew into a full blown family feud, although the Dinklebergs do not seem to be aware that the Turners hate them, and the Turners' themselves rarely openly show this to the Dinklebergs, instead opting to growl behind their backs or engage in "friendly" competitions (which the Turners usually always lose because of Timmy).
Mr. Turner and Sheldon have been one-sided "rivals" since childhood. Before Mrs. Turner married Mr. Turner she dated Sheldon. However, when Sheldon Dinkleberg struck rich by inventing parachute pants, he quickly dumped Mrs. Turner for a more extravagant life. It is unknown how or when he met Mrs. Dinkleberg.
Mr. and Mrs. Dinkleberg currently live right next door to the Turner house (which is due to Mr. Turner throwing a For Sale onto the house that the Dinklebergs live before they got to it), their house is bigger, more expensive, and is kept in better condition than the Turners'. Mr. Turner once attempted to destroy Sheldon's house with a rocket launcher that Timmy brought from inside the television, but it was out of ammunition, so he and wife left to go get some while they left Timmy punished and miserable due to Vicky framing him for things he didn't do. Timmy got so angered that he decided to run away into television. Mr. Turner did come back with ammunition, but it is not known if he launched any of the rockets at Dinkleberg's house. Timmy's dad once got so enraged about three things happening in one day (his ties having different colors, no milk in the milk carton and the weather saying it is going to be rainy on the newspaper even though it is sunny outside) that he launched Operation Dinkleberg by re-modeling Timmy's room into a spy headquarters. Dinkleberg seemed to be evil at first (as shown close to the end) but in the end, he was only pretending to be evil to make Timmy's dad happy. He gave Timmy a new bike and some money and he told Timmy to buy his dad some new suspenders since for most of the episode, he had his pants down.