Bryn Magus was the commander of the battlestar Galactica, father of Iphigenia and Paulus, and a father-figure to Lt. William Adama. Some time prior to the Cylon War (as depicted in the game), Adama's father often saved Magus' life; when Adama was orphaned, Magus looked after the boy as part of his debt to the elder Adama, later welcoming him onboard Galactica when he graduated from flight school.
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.
Note
The "Battlestar Galactica" video game has its own continuity that uses elements from both the Original Series and the Re-imagined Series.
In some write-ups of the game, his name is written as "Magnus" (Latin for "great"). However, the write-ups are in error, as in the game he is clearly named Magus.