Bryn Magus was the commander of the battlestar Galactica, father of Iphigenia and Paulus, and foster-father to William Adama. Some time prior to the Cylon War, Adama's father often saved Magus' life; when Adama was orphaned, Magus welcomed him onboard the Galactica.
After the sneak attack at the start of the War, Magus and other Colonials spent a year in a Cylon prison camp before being liberated by the battlestar Perseus.
In some write-ups of the game, his name is written as "Magnus" (Latin for "great") but this is a mistake, as in the game he is clearly called Magus.