Sergeant Major (SGM.) Alvin Moore was a sergeant in the United States Army and a recruiter for the ROTC program. He was also Angela Moore's father. He and his daughter had a slightly strained relationship due to his constant duty to the army, and the fact that Angela's mother left them when Angela was young.
SGM. Moore first visits Angela at Pennbrook (in Angela's Men) when he is sent to recruit some students to the ROTC program. While there, he sees how unhappy Shawn and Angela are and, hearing of their past, reunites them. He also leads a group of students, which includes Shawn, Cory, and Eric, through an ROTC training program. It is difficulty leads to the resignation of everyone. From the experience, he takes an interesting perspective of Eric.
He returns in Angela's Ashes with news that he has been reassigned to Europe for a year. He offers to take Angela with him, and, following an emotional decision by Shawn, departs for Europe with his daughter. While there, though, he enjoys giving Eric a hard time.
Based on his insignia he is actually either a Master Sergeant (MSG) or a Sergeant Major (SGM). When he first appears in Angela's Men there is a star in his rank insignia indicating he is a SGM, but in Angela's Ashes there is no star but still the sergeant stripes with 3 "rockers" underneath indicating he is only a MSG.
Angela mentions in the Girl Meets World Season 2 episode "Girl Meets Hurricane" that her father passed away on a fishing trip.
Julius Carry, who played Alvin, died in 2008.