Green’s Dictionary of Slang

a sycophant, a crawler.

1877		Swinburne letter 7 Sept. (1960) IV 18: I am infinitely amused at the idea of your asking Mr. Bumsucker Walford (excuse the Rabelaisian term current at our universities to define a sycophant) .
1943		‘George Orwell’ in Coll Essays II 266: The lords of property and their hired liars and bumsuckers .
1962		Paton & Shah Sponono I i: So you got your badge, your bumsucker’s badge.
1989		H. Rawson Dict. of Invective (1991) 376: To be a sycophant, or in British English, dating to at least the nineteenth century, a bumsucker.