Joel Rosenbeg's Guardians of the Flame
Guardians of the Flame is a long-running series by author Joel Rosenberg and is arguably his best-known work. The series is about a group of college students who participate in a fantasy role-playing game, and are magically transported to the world of the game by their gamemaster.
The first book, The Sleeping Dragon, focuses on the former students struggling to survive in the world of the game. The series progresses with the students choosing to live in the 'game world' and forming their own community, which is in part based on opposition to the ubiquitous slave trade.
In the later books, the focus shifts from efforts to destroy the slave trade and on to various characters dealing with the changes in the fantasy world wrought by the former students (now mostly 40-somethings). The final three books shift focus to a new set of protagonists, relegating the 'Other Siders' to supporting cast and cameo appearances.
Louis 'Lou' Riccetti is one of the students. Originally, after reaching This Side, he was a somewhat powerful wizard called Aristobulous. He gave up his wizardly powers to revive his comrade Ahira from death, promising to use his skills as an engineering student to technologically revolutionize This Side. He succeeds to an amazing degree, introducing things such as gunpowder and the telegraph. He is known as the Engineer and has begun to train students to go into the world and create. To date, he is still alive.