Ian may not be as intelligent as his brother Lip, but he is more physically fit. He is described by Frank to having an excellent work ethic in nearly everything he does. He is often uncertain of what he wants to do in his life, but once he makes a goal for himself he goes after it 100 percent. He is also self-conscious of his bipolar condition, which he inherited from his mother and often feels inadequate as it prevents him from certain things. Sometimes refuses to admit that he has a problem when his condition causes him to go off his usual path.
Ian gets along with all his siblings who were aware of his sexuality long before he revealed it and accepted it regardless. He is closest to Lip and Fiona but does get along with his younger siblings and often helped shield them from Frank's influence. He was devastated by the betrayal of Sammi who told the army of his AWOL choices. However, he did try to redirect her son Chuckie from his misguided views from juvie. Ian like his siblings resents his father Frank for his neglect and treatment of him since his mother Monica left them. For some time, he felt his father despised him the most.
Although, he was greatly surprised to learn Frank wasn't even his biological father but rather his uncle. After meeting his presumed father Clayton Gallagher, Ian chose not to broach the subject and accepted Frank as his father, just as Lip and the others are his siblings. Interestingly enough, Frank also claims Ian is still his son while not scorning his sexuality and accepting him no matter what. Despite stating he hates him, Ian was worried when Mickey plotted to kill Frank for discovering he was gay.