The Ambassador is a named Psycho in Trauma Loop wielding a ZKZ Transactional Rifle. It can be found at the top of a spiral staircase in the tower of the left path. Since it uses the Transactional Rifle, it's capable of dealing immediate death to the player if allowed to fire even once.
The Ambassador's sniper perch is positioned to overlook the path through the level that comprises an outdoor platforming section leading to a series of wood shacks and toxin vats, from which he can snipe at the player from outside the game's draw distance. This section leads to the Biojet upgrade but is extremely difficult to pass through while the Ambassador is still alive.
When the Ambassador is killed it does not reappear unless the game's save data is erased or modified, even if you restart the mission.
On Hope Eradicated difficulty an identical Psycho appears beneath the bookshelf elevator in the left path. This one is not named and will reappear every time the mission is started on Hope Eradicated difficulty.