Norvo Tigan was the younger brother of Ezri Tigan and Janel Tigan, and the son of Yanas Tigan. He and Ezri had a close relationship; he even used her childhood nickname, 'Zee', when addressing her. He was not nearly as close to the rest of his family.
A brilliant but discouraged young artist with a quiet, sensitive manner, Norvo was an easy target for his controlling mother. Norvo was resentful of Yanas' constant criticism and refusal to acknowledge his worth. In 2375 he finally snapped, and murdered Morica Bilby, a friend of Miles O'Brien and a woman who was pressuring the family for more money. When Ezri discovered this, she blamed her mother and herself, her mother for her controlling ways, and herself for not seeing her brother's problems earlier. Norvo was sentenced to thirty years in prison for his crime. (DS9: "Prodigal Daughter")
Norvo's situation evidently played on Ezri's mind, as after being ruthlessly interrogated by the Breen later that year she deliriously rambled, "I'm not just saying this because I'm your sister. You have a gift." (DS9: "'Til Death Do Us Part")