Artimus Entrari. From Forgotten realms series. He is usually fighting Drizzt Du’urden .

The Scarlet Pimpernel.

^^^^actually, I am wrong on the above.

@zenvelo, right—he wasn’t an assassin. He rescued people from the guillotine.

I don’t know about “most interesting,” but in the Dresden Files series, Harry Dresden came up against some pretty lethal villains. I stayed with the series for maybe 16 titles, and I was impressed by the author’s knack for thinking up so many different varieties of deadly menace.

^^Did wonder about it. A long time ago I saw this black and white classic film and can’t recall if the Scarlet Pimpernel was an assassin or something else.

@mazingerz88, that was the Leslie Howard version, I’ll bet (1934). Great movie. Howard played Sir Percy Blakeney, who posed as an air-headed British aristocrat while leading a secret life smuggling would-be victims of the reign of terror out of France. Merle Oberon played his French wife, who didn’t know his secret.

Bobo Fett. He was an assassin and a bounty hunter. From Star Wars. I don’t know what Star Wars novel that he was in. I usually only watch the movies.

The “most deadly” seems like a silly thing to try to ask, and it has a suitably silly answer, maybe, in John Wick. In a fantasy world filled to the brim with exaggerated assassins, he out-assassins three (going on four, so far) films (and yes, there are books and comics, since you did ask about reading) full of assassins in nearly non-stop assassin versus assassin assassination. How more assassin can you get?

Well, I guess you could assassinate on a larger scale, particularly in sci fi books such as the Honor Harrington series. Just goes to show though how it may be pointless to try to compare for “most deadly”.

And “most interesting” seems like almost entirely a matter of personal taste, and there are too many too choose between.

Some who come to mind:

The Jackal in The Day of the Jackal (an interesting realistic assassin)

Gavrilo Princip of The Black Hand (one of the most impactful assassins, interestingly sparking off World War One)

Hattori Hanzo (historically noteworthy ninja)

Harmodius and Aristogeiton were interesting in that their failed assassination of the tyrant Hippias led to Athens becoming pro-tyrant assassination in principle.

The murderer in Agatha Christie’s final Hercule Poirot book Curtain might count as a particularly interesting assassin. Poirot certainly thought so.

I’ve always been partial to the killer in And Then There Were None, but maybe you don’t consider murder mystery murderers assassins?

Some non-literary examples:

A large amount of the plots of the classic TV show The Avengers is about bizarre assassins of various types.

Barry is a funny recent comedy TV series about an assassin.

(Oh I guess there are only John Wick comics, not actual books… probably for the best!)

Agent 47, no doubt.

Girl with the Dragon tattoo.

Thufir Hawat.

I like Lawrence’s Grey Sisters.