Anime Bass was born of the remnants of PharaohMan's data, which were extracted from the Navi by Wily, who wanted his Ultimate Program. Bass had no memories of his previous life as PharaohMan until he abducted MegaMan and read his memories, learning his origins and awakening his "true self".
Bass attempted to consume the data of Gospel (Grave in the English anime), for the two shared the same origin, to become whole, only to be consumed himself. When MegaMan destroyed Gospel and restored all the NetNavis devoured by the beast, Bass took residence in Shuryou Gospel's (Kid Grave in the English anime) android body. He left, vowing revenge against the world. He reappeared as the creator of the robot Allegro in Axess, and tried to absorb MegaMan and ProtoMan's Ultimate Programs at the beginning of Stream. He was easily defeated by Slur and imprisoned in the UnderNet, losing his means of travel through the human world in the process. In RockMan.EXE: Program of Light and Dark, a film exclusive to Japan, Bass is captured by Dr. Regal and is brainwashed to obtain the Tadashi Hikari Program, and fights MegaMan and Colonel. Bass, upon returning to normal, wanted to make Regal pay for the "disgusting act" of a human using him as a pawn, even if meant siding with MegaMan. The duo were no match for Nebula Grey, so MegaMan opted to have Bass absorb his Ultimate Program. The resulting BassCross eliminated Nebula Grey, but Regal summoned a black hole in a last ditch effort to destroy the Navis along with himself. Bass flung MegaMan out of harm's way as he himself got sucked in, ultimately absorbing Nebula Grey's power, which proved vital in his rematch with Slur. The tables had turned, and he deleted her, impaling her through the chest on his arm and suffocating her. He vanished, and his current whereabouts are unknown.Manga In the manga, Bass made his first appearance in Volume 3, when MegaMan and Protoman were investigating the UnderNet. Similar to his game counterpart, he faced Serenade in the past, and was determined to wield the same power one day. Constantly coming into conflict with MegaMan, ProtoMan and their operators, Bass would eventually be taken away by Dark MegaMan (Dark Rockman) and LaserMan, who had intentions to change the world into the Dark Kingdom. Dark MegaMan subsequently tried to absorb all of Bass' power to become the ultimate being, but, failing to consume his entire consciousness, was disconnected from the Navi's soul. Bass was then seen rescuing Colonel from Nebula Grey. Bass proceeded to attack Nebula Gray, but to no avail, leading him to fuse with MegaMan to create BassCross MegaMan, though he ultimately broke away from the Navi to destroy Dr. Regal's submarine. He disappeared, reappearing years later to rescue MegaMan from a super-virus. He reappeared in the underground during the fight to see who could control Cyberbeast Gregar. He once again saved MegaMan, this time from Cyberbeast Falzar. Bass had stopped the attack on MegaMan, and then absorbed Falzar to once again be MegaMan's equal in terms of power. After the cybeast merged and slowly deleting the real world, Bass eventually assisted MegaMan, after encouraged by Serenade, who kept telling if MegaMan is his first and only friend. Compared to the anime and the game, Bass is portrayed having deeper rivalry and friendship with MegaMan. (Source: Wikipedia)