In Teen Wolf, a löwenmensch is a species of shapeshifter. It is the hybrid of a wolf and a lion.
Löwenmenschen function similarly to their werewolf, or coyote cousins in the fashion that the same shapeshifter hierarchy exists within their genome: they can be classified as an alpha, beta or omega with the respective eye color.
The attributes they gain from their lion side are currently unknown. Though in the natural world, lions live in prides, thereby suggesting a lion shapeshifter could gain the same power amplification from being a member of a similar family group, similar to a werewolf in a pack.
The only löwenmensch to appear in the series is Garrett Douglas, or 'Hauptmann' who is a main antagonist of Season 6. He was an alpha and sought to take over the Wild Hunt for his own ends.