Rudolph Isley, one of the founding members of the legendary soul group The Isley Brothers, died Wednesday at the age of 84, TMZ reports. The singer’s cause of death was unclear but a person close to the situation told TMZ he may have had a heart attack. In 1954, Rudolph teamed up with his brothers, Ronald, O’Kelly, and Vernon, to form The Isley Brothers. Their debut single, “Shout,” was an immediate hit, and they continued to make music for over five decades with other hits including “Twist & Shout,” “This Old Heart of Mine (Is Weak For You),” and “Footsteps in the Dark.” Rudolph made headlines in March when he sued his brother, Ronald Isley, over the group’s trademark, claiming Ronald intentionally registered it as an individual, pushing him out from his share of the asset. He said he was “unaware of the degree to which Ronald exploited the Mark, the licenses and/or other transactions that Ronald entered into.”