Animals of various shapes and sizes have long been part of ancient religions and thus saturated the culture of many peoples around the world. There is no doubt that wolves have been part of rituals long before recorded history. However, werewolves are not wolves. They’re people, and they spend most of their time in human form, only transforming at a certain time of the month. That’s their trademark.
Given this parameter the first recorded case of people transforming into wolves comes to us from the Greeks (our first organized recorders of history). Greek mythology tells the story of Lycaon, a king of Arcadia, who decided to test Zeus by making him a nice meal of a child’s flesh. Zeus, terribly angered by this, punished him by turning him into a wolf. There are several different version of the story, some of which involve not only Lycaon but also his 50 sons being turned into wolves, but all involve Zeus’ wrath in the form of transformation into a wolf.
This myth lead the citizens of Arcadia to adapt an annual ritual called Lykaia which involved the testing of young adolescent males coming age by the offering of human flesh from a victim of sacrifice. It was said that whoever ate the human meat would turn into a wolf and remain so until they abstained from human flesh for nine years. Although this ritual and the myth it’s based on are presumably metaphorical and not literal the stories of such events tell that people actually turned into wolves. These early rituals and their stories paint the scene for much of the werewolf story common today: nocturnal transformation into a wolf, the consumption of human flesh, and the bestial behavior of werewolves.
In addition to Odin’s story of the Arcadia kingdom there also reports of men turning into wolves from Virgil, Pliny the Elder and Agriopas. From there, the mythos of the werewolf spread throughout Europe and the world through verbal tradition and mysticism.
Like zombies, vampires and witches the specifics of werewolves vary from region to region so you might get a different story about how a werewolf comes into being, how to identify a werewolf when not in wolf form, and how to cure or kill a werewolf. Modern culture with all the movies, stories, and other forms of entertainment where you find werewolves maintain these differences, illustrating the contrasting styles of depicting wolves as cursed or evil.
However you cut it they are part of the pantheon of monsters we hold near and dear, and therefore part of the scariest holiday and all that comes with it.