"I was never supposed to know any of this."
-- Jacob Kowalski (WFT)
No-Maj factory worker in the 1920s. He fought for America in World War One (WFT).
In 1926 Jacob went to a bank in New York City to get a loan for a proposed bakery based on recipes he learned from his Grandma. While waiting to meet with the bank manager, he met Newt Scamander, who was searching for his lost Niffler. As they interacted, their similar suitcases became switched so that Newt ended up with a case full of pastries, while Jacob walked away with a box full of dangerous magical creatures (WFT). Ex-Auror Tina Goldstein saw them at the bank and became suspicious, ending up later with Newt at Jacob’s apartment where he had been bitten by a Murtlap. Due to his injuries, Tina took Jacob home to keep under observation overnight along with Newt, who was still missing several creatures that had escaped from his case.
Jacob was allowed to visit the menagerie inside Newt’s case, as well as MACUSA headquarters in the Woolworth Building due to his involvement in the missing fantastic beasts. While amazed at what he saw in the magical world, Jacob took everything in stride and was soon good friends with Newt Scamander, who couldn’t bring himself to Obliviate his companion.
When Jacob met Tina’s sister Queenie he was quite smitten — he enjoyed her cooking and did not mind that she could read his mind using Legillimency. They carried on a sweet romance in spite of the fact that Jacob was a No-Maj and forbidden by MACUSA laws to be friends with a witch. After the attack on New York by an Obscurus, however, Jacob agreed to erase his memories like the rest of the No-Majs by standing in the Thunderbird rain containing venom from the Swooping Evil (WFT).
Newt managed to secretly help Jacob by giving him a suitcase full of silver Occamy eggs to finance his bakery, and Queenie visited his establishment where he sold cookies shaped like some of the beasts he helped to recapture such as the Erumpent, the Occamy, and the Demiguise (WFT).
Jacob hated working at the cannery because his real talent was baking, which he learned from his Grandma.
Jacob is a good-natured, ordinary American guy, and functions as a literary device known as the "Everyman" - a normal character through which the reader or audience learns about extraordinary things and situations. We can identify with him because he has no magical powers or magic wand, and thus we also feel his sense of loss when he has to lose his memories and leave Queenie. However Jacob seems to have a power of his own since he somehow remembered the creatures enough to bake look-alike cookies after opening his bakery. ~ SIP