Kendall Jenner's being flooded with letters from a fan who claimed to love her at first, but then turned bitter, angry, and she thinks ... dangerous.
According to new docs ... a California man named Thomas Hummel has been incessantly professing his love for her since February. Kendall's security warned him in March to stay away, but a few weeks later he started writing again with a much darker tone.
According to the docs, Hummel started insulting Kendall and her mother, Kris Jenner. In one letter, he called Kendall "an internet whore, cackling your way through life." He continued ... "You look like you've been f***ing AHOLE Dog Sh**t in the sewer for years." He also accused Kris of paying A$AP Rocky -- or as he puts it, "AHOLE Rockhead" -- to sleep with Kendall.
In other bizarre letters ... Hummel mentions remembering Kendall from the post office in 2008 and Costco in 1998 and falling in love with her then. She would have been 13 and 3 years old at those times.
Kendall ran to court to request a restraining order, and the judge granted it. Hummel must cease all contact and stay at least 100 yards away from Kendall.