The Ultra Rangers are groups of insane people wearing skin-tight, vibrantly colored suits. They're found among ghouls and are always fighting each other and the ghouls around them, presumably because of territorial reasons.
The Ultra Rangers' past is unknown, but it is believed that they are indeed human due to their humanoid speech patterns.
The Ultra Rangers make several appearances in the Fallout 4 videos, both streams and mod reviews. They are found around packs of ghouls, usually fighting those ghouls and themselves. They usually carry laser swords, though they have been also found to have the ability to shoot guns.
The Ultra Rangers seem to hate themselves and what they are, if what Al says is to be believed. The different colors, White, Red, Blue and Yellow are always found fighting themselves, typically ignoring Al until one emerges as the victor. Al usually stands aside and watches them, laughing at the battles between them.