A GMPC, or "game master player character," is sometimes a pernicious form of self-insertion by the GM in which an NPC not only outshines the PCs in ability but seems to have greater importance. Such a character is often a Mary Sue but could simply be a poorly conceived ally for the PCs. Many GMPCs were not intended as such, but may have arisen out of a sincere desire to participate. In the hands of a capable GM, however, who does not set out to outshine the other players but to supplement them, a GMPC may be a valuable addition who complements the group by providing additional skills the group's existing characters may lack. When a GM is careful to keep the GMPC to the back of the group and not in the spotlight, the main problems of the GMPC are negated.