Tenken is the manifested spirit of Sajin Komamura's Zanpakutō that is seen during the anime-exclusive Zanpakutō Rebellion and the subsequent Tōjū Campaign.
Despite his mighty and intimidating appearance, he appears to be a very calm individual, having yet to lose his cool. According to Gonryōmaru, Tenken seems to be incredibly shy, like his Shinigami wielder, which explains why he doesn't normally talk. So far, he has only spoken once, saying the word Bankai in a deep echoing voice.
(Source: Bleach Wiki)