J. Jenks is a full-time lawyer and part-time purveyor of illegal documents in his fifties. He has worked with Jasper Hale since the late 1980s.
J. Jenks was born sometime in the 1950s, in Seattle, Washington. He is known in certain circles as being one of the best document forgers available. He has worked with Jasper Hale since the late 1980s; his old partner and mentor knew Jasper for fifteen years before him.
He has Max run the downtown office as a contact point for criminals who need legal documents, and conducts legitimate business as "Jason Jenks", an attorney with a fancy office in a skyscraper in Seattle, and as Jason Scott, an attorney with a modest practice in the suburbs.
J is aware that the Cullen family are supernatural, having noticed that Jasper never ages, but does not know that they are vampires. Because he is paid well, and because Jasper has manipulated his emotions to ensure his fear of the Cullens, J always gives him top priority and does not talk about his family to others.
In Breaking Dawn, Alice left J's downtown address to Bella, which led her to Max, Jason's agent, who in turn sends her to him. Initially he assumed Bella was Jasper's wife, leading Bella to think that Alice gave her the address and that Jenks had no idea what Alice looked like.
Later on, during the second meeting with Bella, he is told that she is the wife of Jasper's brother, and he wishes her and the rest of the Cullens' happiness and health. Bella employs him to forge birth certificates, passports, and a driver's license for Jacob and Renesmee. Over the course of their relationship, he becomes more relaxed with Bella than he is with Jasper. An honorable man, he is under the belief that she intends to use them to kidnap Renesmee from her father, and despite his fear of the Cullen's retribution, he initially expresses reservations about giving her the requested documents. Bella assures him that this is not the case. She afterwards decides to take over all relations with him in order to spare him any further stress.
In Breaking Dawn - Part 2, Jasper visits J to give him instructions to forge legal documents for Renesmee and Jacob, and by the time Bella contacts him, he has already finished with the orders. He delivers the documents to Bella at a public restaurant.
J is described as short and balding, paunchy, probably at least fifty five, he is also trembling, blanched to a sickly paste color, with sweat beading on his forehead. He also wears expensive clothing. In the movie, he is African American, with black hair, dark skin and mustache, and slightly overweight.
He appears to be a very nervous man, mostly due to his fear of Jasper, provided by his power to control his emotions, and by extension, any other member of the Cullen family. The bad reputation of his forging activities notwithstanding, he is an old man with a kind heart, and is very careful with whom he deals with.
His movie counterpart is calmer, but he still holds utmost respect for the Cullens and their business with him.