Sub-Visser Twelve is a rank in the Yeerk military hierarchy.
Esplin 9466 was promoted to this rank from Sub-Visser Seventeen. He was especially proud of this promotion, as it meant skipping five ranks, advancing him quickly up the Yeerk hierarchy. To achieve this feat, Sub-Vissers Thirteen through Sixteen were promoted, killed or executed. (What happened to the old Sub-Visser Twelve is never clear.)