The book doesn't specify if the monster was created by one man or several or how he was brought to life. I think we can safely guess that the monster was brought to life using electricity because it has such an influence on Victor. SPOILER ALERT. I would also say that is safe to say that the monster was probably created using more than one man because later on Victor tears apart/destroys the monster's companion before he completes her creation. These are just my thoughts and if anyone has anything else they would like to add please comment
She began writing what she assumed would be a short story. With Percy Shelley's encouragement, she expanded the tale into a full-fledged novel.  She later described that summer in Switzerland as the moment "when I first stepped out from childhood into life".  Shelley wrote the first four chapters in the weeks following the suicide of her half-sister Fanny.  Byron managed to write just a fragment based on the vampire legends he heard while travelling the Balkans , and from this John Polidori created The Vampyre (1819), the progenitor of the romantic vampire literary genre. Thus two legendary horror tales originated from the conclave.
The script for the film, by Don Bachardy and Christopher Isherwood , was published in paperback as a tie-in.  The script contains a prologue in which Mary Shelley is telling her tale of horror to Percy Shelley and Lord Byron , as Dr. Polidori sulks nearby.  As she reaches their parts in the tale, they rush to join the main action and the story proper begins. Some shots in the film indicate that at least part of this prologue may have been filmed. If this segment had been included, it would have featured Nicola Pagett as Mary, Leonard Whiting as Shelley, David McCallum as Byron, and James Mason as Polidori.