Short answers, pulled from the story.
The main character is Holger Carlsen, an American-trained Danish engineer who is the reincarnation of Ogier the Dane. He is transported from 1943 to a parallel universe where he becomes a knight of the Middle World.
Holger Carlsen left his original timeline on the 2nd of May 1943 when he was struck by a bullet near Elsinore. He spent five years searching for a medieval spell to return to his own world after being trapped in the Middle World.
The shield bearing three hearts and three lions defines Holger Carlsen's destiny across two worlds. It represents his role as a knight of the Middle World and his connection to the eternal struggle between Law and Chaos.
Three Hearts and Three Lions inspired the original alignment system in Dungeons and Dragons which grouped characters and creatures into Law and Chaos. The novel's depiction of the regenerating troll became a staple of the game's monster lore.
Holger Carlsen failed to reunite with Alianora because he spent thirty years trying to return to her after being stranded in the Middle World. When he finally reached her, she had accepted the proposal of a village smith and given birth to two sons and a daughter.