What does it mean that this guy, the father of Joey's college roommate, is unnamed, when our narrator specifically tells us his wife's name is Tamara? And why don't they have a last name either? Well, let's look at him a little more closely.
The first thing we learn about Jonathan's father is that he is "the founder and luminary president of a think tank devoted to advocating the unilateral exercise of American military supremacy to make the world freer and safer, especially for America and Israel" (3.2.14). He later boasts at the dinner table that he and his friends had been personally pressing President George W. Bush to invade Iraq and to "learn to be comfortable with stretching some facts" in order to achieve that goal. This suggests that he is a neoconservative and also means he might be part of the pro-Israel lobby in Washington. With that in mind, we might assume that Franzen intends for him to be a faceless figure, a mysterious puppet master who controls the strings of war and peace in our lives.