Jokubas is the guy Jonas knew back in Lithuania who immigrated to Chicago years ago. Although Jonas is sure that Jokubas has struck it rich here in the States, it actually turns out that Jokubas is barely making ends meet by running a delicatessen in Packingtown. Jokubas has a very small practical role in the novel: he, like Grandmother Majauszkiene, is here to introduce Jurgis's family to American life. Unlike Grandmother Majauszkiene, Jokubas is not totally skilled at navigating around Packingtown. Jokubas helps them out when they first arrive, but he cannot save them from making disastrous mistakes such as buying a shabby house for too much money.
Jokubas does manage to get Jonas a job at a meatpacking plant. He also takes Jurgis and the rest of the family on their first tour of the slaughterhouse industry. Jurgis and his family are dazzled by the show of efficiency and productivity they see at the stockyards. Jokubas warns them that he has heard bad stories of disease coming out of these meatpacking plants, but Jurgis and the rest don't believe Jokubas at first. Jokubas is also the one who tries to help Teta Elzbieta read the deed to the house they wind up buying. But he isn't as familiar with English legal speak as Grandmother Majauszkiene, so he misses that key clause about interest payments that winds up ruining Jurgis's family. Jokubas means well, but he is as caught up in the capitalist machine as any of them. He doesn't have a magical key to success that will help save Jurgis or his family from disaster. After Jurgis's family starts to fall into debt, Jokubas disappears from the novel. His role in the book is to introduce Jurgis's family to the capitalist system. Once they are caught up in it, his part in this drama is over.