The empire reached its greatest territorial extent under Askia Dauoud.  
One legend tells that the first king of the kingdom that grew into this empire was a Yemeni stranger who defeated a monstrous fish and founded the Dia dynasty.  Court officials in this empire included the hugu-korei-koi and the wanadu, and one important military position was the hi-koi, or "commander of canoes".  The empire reached its greatest territorial extent under Askia Dauoud.  A coup against Sunni Baru brought to power its greatest leader, Askia Muhammad.  FTP, name this African empire established by Sonni Ali from the Kingdom of Gao, containing great centers of learning such as Djenne, which succeeded the Mali.
One legend tells that the first king of the kingdom that grew into this empire was a Yemeni stranger who defeated a monstrous fish and founded the Dia dynasty.  
the {Songhai} Empire (prompt on early "Gao")