Tax gene product, commonly referred to as Tax, is an essential protein encoded by the HTLV-1 (Human T-cell lymphotropic virus type-1) virus. It plays a crucial role in the replication and pathogenesis of HTLV-1. Synonyms for Tax gene product include Tax protein, Tax oncoprotein, and HTLV-1 Tax. This multifunctional protein modulates various cellular processes, including gene expression, cell cycle control, and immune response regulation. Due to its significance in the development of HTLV-1-associated diseases, understanding the mechanisms and functions of Tax gene product is paramount. Comprehensive research on Tax is vital for the development of targeted therapies against HTLV-1 infections and associated diseases.