Gonryōmaru is the manifested spirit of Chōjirō Sasakibe's Zanpakutō that is seen during the anime-exclusive Zanpakutō Rebellion and subsequent Tōjū Campaign.
He often refers to people by the -dono honorific, which means lord or master. Also, Gonryōmaru resents his former owner's inability to stand out from other Shinigami. Gonryōmaru also seems to have a particular friendship with Tenken, calling him Tengen-dono, and speaking for Tenken, who rarely talks.
(Source: Bleach Wiki)