It does not sound odd at all, and wouldn't imply that he is the only one.
This use of the fits the following definition as the referent George Soros has been previously mentioned - which son of Satan we're talking about is clear so we may use the definite article.
A. adj. Definite article (determiner).
I. Referring to an
individual item (or items).
- Marking an item as having been mentioned before or as already
known, or as contextually particularized (e.g. They escaped in a car.
The car was later found abandoned or I had some in a jar but it all
leaked out through the lid).
And could be understood through following definition also,
II Referring to a term used generically or universally.
- With a singular noun or an adjective.
b. In predicative use: before a noun or noun phrase of this kind used
to indicate that a person is a notable example of the class.
1761 T. Smollett et al. tr. Voltaire Wks. V. 82 In reading the
history of Henry IV. by father Daniel, we are surprised at not finding
him the great man.
1767 A. Young Adventures Emmera I. iv. 13 I am often surprized you
should have treated so coldly a man so much the gentleman.
1838 M. M. Sherwood Henry Milner iii. ix. 175 He is a genteel
young man—no snob—quite the gentleman.
1897 A. R. Marshall ‘Pomes’ from Pink 'Un 8 She was quite the
lady In deportment and dress.
1925 L. H. Myers Clio i. 8 Marie, golden-haired, short-skirted,
very much the soubrette, began tripping about the room.
1934 P. Lynch Turf-cutter's Donkey xiii. 101 Isn't he the
1955 ‘P. Dennis’ Auntie Mame iv. 62 In the process of coaching the
kid, the old girl became quite the athlete herself.
2000 K. Charles Cruel Habitations (2001) xv. 283 ‘Oh, bully for
you,’ she sneered. ‘Aren't you the noble one?’
The Cambridge Grammar of the English Language comments on similar uses of the on p369
Under certain circumstances, however, the definite article can be
appropriate with a count singular even when the context does not
strictly limit the number of entities satisfying the description given
in the nominal to just one:
i Put your cup down on the arm of your chair.
ii He married the daughter of his bank manager.
An (arm-)chair has two arms, but the definite article in [i] is in
order on the assumption that it doesn’t matter which one you choose.
Again, then, the definite article signals my expectation that you
don’t need to ask Which arm of my chair? In [ii] it could be that
the bank manager has in fact two daughters, but the is again
appropriate on the assumption that you don’t need to ask Which one?:
perhaps the other is already married, or too young to marry, perhaps
you don’t know that there are two, and perhaps it simply doesn’t
matter, the important point being only that his bank manager was the
father of the woman he married.