Lamkin

"Lamkin" or "Lambkin" (Roud 6, Child 93) is an English-language ballad. It gives an account of the murder of a woman and her infant son by a man, in some versions, a disgruntled mason, in others, a devil, bogeyman or a motiveless villain. Versions of the ballad are found in Scotland, England and the US.
According to Roud and Bishop (2012): 
"Lambkin" is not one of the major league Child ballads in terms of popularity, but it was widely known in England and Scotland, and even more so in North America. ... The central character's name varies considerably, including, in just the English versions 'Lambkin', 'Lamkin', 'Lincoln', and 'Limkin', and he is various referred to as 'Long', 'Bold', 'Cruel' and 'False'.
They cite the analysis of Anne Gilchrist, who identified two threads: one Scottish, which retained the mason narrative; one Northumbrian, which lost the mason in early versions, thus encouraging singers to supply a different back-story. Versions collected in England stem from the Northumbrian thread.
A bogeyman.
Other versions follow the same basic story, but the antagonist has many different names, among them "Long Lonkin", "Balankin", "Lambert Linkin", "Rankin", "Long Lankyn", and "Lammikin". Later versions lose the opening of the story, which explains that Lamkin is a mason who has not been paid; in these, Lamkin becomes a sort of a bogeyman who dwells in the wild places; the lord, before leaving, warns against him:
These versions add peculiar incidents that add to the grisliness of the crime. Lamkin and the nursemaid collect the baby's blood in a basin which, along with the idea that the name Lamkin or Lammikin indicates the murderer was pale skinned and, therefore, perhaps a leper who sought to cure himself by bathing in the blood of an innocent collected in a silver bowl, a medieval cure.
In literature.
The ballad, as "Long Lonkin", was taken from a friend by Letitia Elizabeth Landon and published in her "Fisher's Drawing Room Scrap Book", 1835.
The song was referenced in the title of the short story collection, "Long Lankin", by John Banville. The American poet Robert Lowell also referenced the song in the title of his Pulitzer Prize-winning collection of poetry "Lord Weary's Castle" (1946). The song inspired the young-adult novel "Long Lankin" (2011) by Lindsey Barraclough.
A sadistic character named Lankin appears as a member of the Fairy Queen's court in Terry Pratchett's "Lords and Ladies".
Long Lankin appears in Jane Yolen and Midori Snyder's book "Except The Queen".