"This is a German flamethrower. He is armed with a Flammenwerfer 35 and can set things on fire.. soldiers included."— Official game quote
This is the German Flamethrower unit. While he looks pretty ugly with those bottles on back and pipe in front, he IS dangerous. When he will get enough close, he will pull the trigger and try to set your troops on fire. When on fire, troops will run around, potentially setting fire to other soldiers. They will eventually die, leaving a charred body.
The flamethrower's weapon is also dangerous to both himself and units friendly to him. If he is shot in the tank, KABOOM!! His life and the lives of those around him will end in flames.
This dude is easy to kill while advancing because he moves at the same pace as other Germans, and needs to get close to your units before firing. Sometimes when he is shot, the bottles of flammable liquids on him can explode, gibbing him, and setting nearby units and dead bodies on fire. But if he gets close to a bunker and manages to fire, you may encounter some serious problems. Don't worry if your men are over 200 pixels away, he is useless at that range, but his range may sometimes deceive you.
In real life flame throwers would not actually explode unless the bullet hitting the tank was incendiary. (meaning an extremely low probability of the tank exploding) This meant all that cool stuff you saw in movies was a load of BS used to make the movie more exciting. If someone were to shoot in the tanks one of two things would happen A. you would hit the fuel tank and now fuel was leaking all over the place B. you hit the air tank and the operator would be thrown in one direction, which could be rather comical if you like dark humor.
Flamethrowers were not very common in WWII because they didn't fit into the strategy of Blitzkrieg. Both their immobility and short range were disadvantageous in the open battlefield. They have been used successfully only in sieges of cities in Soviet territory (known as Kesselschlachten). In constructions, due to the trapped air and the gunpowder residue inside them, the flamer's flame will be several times more potent.