"Is the robotic sidekick that normally travels with and aids Clank within the Rachet & Clank series
Clank, who was originally from a robotic line designed for causing destruction but accompanies Ratchet due to the robot line's assembly computer altering him for purposes of good.
Clank sits on Ratchet's back (in a backpack-like fashion) and is used to provide useful jumping, hovering, and diving abilities through various upgrades. These upgrades are given over the course of the first game in the series, but Clank retains them through the later ones."
Source: Wikipedia, "Rachet_and_clank", available under the CC-BY-SA License.