Jeff Difford, usually called Pastor Jeff, is a pastor at the church Sheldon and his family attend in the series spinoff Young Sheldon. Sheldon considers Pastor Jeff an enemy of his and enjoys forcing Jeff to engage in lengthy debates over the credibility of Christianity.
Sheldon harbors anger towards Jeff for spewing pro-Christian principles having gained multitudes of followers and refusing to allow even one atheist voice (Sheldon himself) to defend how science can contradict religion.
Pastor Jeff is a devout Christian who in his debut appearance claims that a God truly exists because it is cynical to doubt so. Sheldon points out the flaw in his reasoning and Jeff enthusiastically gives him a few seconds to elucidate, but then cuts Sheldon off short before Sheldon can talk any more about atheism and science towards the church. This is what makes Sheldon develop a strong contempt for Pastor Jeff.
Jeff is married to a Hispanic woman named Selina although she doesn't speak English causing a language barrier between them. Selina doesn't seem to like Jeff and thinks he failed as a husband. Jeff stole Selina's own credit card for money behind her back because the church is losing money, thus putting Jeff and Selina at the risk of bankruptcy. Jeff tries to keep his financial hardship a secret from Selina fearing that this will make her want to divorce him. Also, Jeff lied or exaggerated to Selina how rich he is.
In S01E15, Sheldon claims that he still vows to destroy Pastor Jeff's comments about Christianity triumphing over atheism after having been denied the chance to do so using evidence of earth's archeology and rock geology.
In S02E15, it turns out that Jeff's marriage with Selena has sunk so low that he tries to stay away from her as much as possible and stay outside his house even when he's sick with a flu.
As the series progresses, it becomes more visually clear that Jeff is more concerned about how much money he can make off of promoting Christianity such as church attendance or church-related activities instead of (or at least not only because of) sincere religious beliefs.
Although he tries to pass himself off as a great, morally superb and reasonable person, Pastor Jeff on the inside is a greedy, insecure liar who will do anything to promote religion because the only way he can make money is to find more people in his town to convert to Christianity to the point he's become reduced to trying to convert children. Jeff even tried stealing money from his wife Selena because the church is on the verge of bankruptcy. Jeff is an unskilled critical thinker. His decision to marry Selena was also a poor one, given that they have a language barrier and the two have nothing in common. Jeff was not financially prepared to marry Selena, yet he exaggerated to her about how well he's doing with money. She leaves him in the penultimate Season 2 episode "A Broken Heart and a Crock Monster", considering him a loser.
- Jeff has a rather bad habit of defending why there are so many gaps in the Bible and Christianity's detailing of the origins of the universe instead of admitting he has no legible answer or he just didn't know of the gaps.
- In a twist of irony, Jeff still is able to get Sheldon to come to church each Sunday in spite of Sheldon being an atheist because he only helps Sheldon maintain a strong interest in destroying religion.
- Jeff's argument in his defense of religion over atheism is based on wishful thinking rather than valid evidence.