Green’s Dictionary of Slang

a wandering beggar, adopting tattered clothing and posing as a madman.

1605		Shakespeare King Lear II iii: The country gives me proof and precedent Of Bedlam Beggars, who with roaring voices, Strike in their numb’d and mortified bare arms Pins, wooden pricks, nails, sprigs of rosemary.
1688		R. Holme Academy of Armory Ch. iii item 68b: Give me leave to give you the names (as in their Canting Language they call themselves) of all (or most of such) as follow the Vagabond Trade, according to their Regiments or Divisions, as [...] Wild Rogues, Mad Men, Bedlams, called also Mad Toms.
1822		R. Nares Gloss. (1888) I 3: abraham-men, or tom of bedlam’s men, or bedlam beggars, A set of vagabonds, who wandered about the country, soon after the dissolution of the religious houses; the provision for the poor in those places being cut off, and no other substituted.
[1910		Dundee Eve. Teleg. 14 Dec. 6/1: A Bedlam Beggar. He accoutred himself in an old blanket and went about as ‘a poor Turleygoot,’ as Shakespeare has it] .