Mosquito

Mosquito was a former Militaires Sans Frontières member-turned rival PF commander after the events of the XOF Trojan Horse operation that destroyed the PMC he formerly worked under.

Biography
Mosquito was part of the MSF Mother Base staff. However, he was kept out of the loop about Paz's survival as well as Chico's capture. When the XOF attacked Mother Base, he ultimately survived, although the events greatly haunted him, causing him to break off from his comrades under the paranoia that the group that attacked Mother Base will send a clean-up squad. Ultimately, the years in isolation were unforgiving to him, which caused his sense of loyalty to be screwed up. He eventually learned of a rumor via an anonymous source, that his former commander in MSF, Big Boss, had sold out his comrades so he could go into hiding, and believed the source to be accurate due to Big Boss being absent from Mother Base that day (in actuality, his being absent was because at the time Mother Base had been attacked, Big Boss had to go over to Cuba to save Chico and Paz), so he decided to form his own Private Force, modeling it after the MSF exactly as it was before the attack and tried to avenge his comrades by attacking the succeeding group Diamond Dogs due to its presumed ties with Big Boss. He deliberately modeled his PF after MSF in every way as he believed it to be the perfect revenge.

In 1984, around the time the Diamond Dogs went to Africa to investigate XOF's activities there and their developing a weapon to surpass Metal Gear, he and his PF made their move, holding their new Mother Base's R&D Platform and several Diamond Dogs members hostage, and threatening to kill them if any Diamond Dogs members attempted to set foot onto their platform. Ultimately, his takeover was quelled by Venom Snake, the leader of Diamond Dogs, who had to infiltrate alone without even indirect aid from Ocelot and Miller due to Mosquito's threats, with his PF being captured shortly after his defeat. He was ultimately a victim of disinformation.

Behind the scenes
Mosquito is a key character in the Main Mission "Retake the Platform" in Metal Gear Solid V: The Phantom Pain. The player can either kill him or otherwise capture him to end the mission. If the latter, Miller will debrief Venom Snake on who the identity of their leader was and his motives for attacking Mother Base, and also let Snake decide how to handle him.

There are 10 side ops that feature wayward soldiers that had formerly been members of MSF similar to Mosquito, although they were depicted as being more significantly unhinged.

He is actually the same soldier who helped Miller to escape Mother Base just before it sank into the ocean in Ground Zeroes.