Jack Lathe is a Muggle-born auror who was originally appointed at Hogwarts in 1975 to investigate several cases of attempted suicide, two of them being Adam McKinnon and Carlotta Meloni. He has been an auror for three years, and was in training the three years previously. Very young for the job, he considers himself a "prodigy".
Jack confessed that his family thinks he is dead, because it is safer for them not to know.
After Death Eater Logan Harper died, Jack was set on probation for weeks. During his probation he visited the Leaky Cauldron almost every day for some Ogden's Whiskey, and while in the Leaky Cauldron he started getting to know Sirius Black and Donna Shacklebolt better. It is speculated whether he fancies the six years younger Donna a bit, but according to Witch Weekly, Jack is rumored to be engaged.
Donna Shacklebolt is heavily implied to have a romantic interest in him.