The term `Ekabrahmana` refers to a ruler who was believed to be equal to a Brahmana, which is the highest rank in the Hindu social system. Among the options provided, the ruler who `Ekabrahmana` has been used for is Gautamiputra Shatkami, which is option 4. It is important to note that the term `Ekabrahmana` was used specifically for Gautamiputra Shatkami and no other ruler from the given options. Gautamiputra Shatkami was a Satavahana king who ruled in the Deccan region of India from around 103-129 CE. He was considered to be a great patron of Brahmanism and was believed to possess qualities and traits of a Brahmana, which earned him the title of `Ekabrahmana`.