Enemy Of The State may not be officially labeled a sequel to The Conversation, but there's plenty linking them together. Francis Ford Coppola had an incredible run of films in the 1970s, including The Godfather, its sequel and Apocalypse Now. In 1974 he made a smaller movie called The Conversation which starred Gene Hackman as surveillance expert Harry Caul. Caul is hired to record the conversation of a couple for a mysterious client, and Harry soon begins to worry his recording could get them killed.
The Conversation is a classic thriller featuring one of Hackman's best performances, and it ends with Harry so overcome with paranoia he ends up destroying his own apartment for fear he's being bugged. Its the kind of bleak, character-driven thrillers that were in vogue during this era, and it ended up being nominated for three Academy Awards. Ironically, it lost the Best Picture prize to The Godfather Part II - another Coppola directed movie.
While the movie ends with Harry still alive, The Conversation isn't the kind of movie that leads to a sequel. That said, Enemy Of The State comes pretty close. This slick 1998 thriller stars Will Smith (Aladdin) as a lawyer who is targeted by rogue N.S.A. agents who through the use of surveillance and planting false evidence ruin his career and life. Smith turns to volatile surveillance expert Brill (Gene Hackman, Superman) for help clearing his name.
Both Enemy Of The State and The Conversation share similar themes, including paranoia over surveillance and technology. Enemy Of The State was directed by the late Tony Scott (Top Gun), so the movie is much slicker and faster-paced. On the surface, Hackman's Brill isn't much like Harry Caul, who was more timid and shy, whilst Brill is outspoken and forceful. Several fan theories have convincingly stated Brill and Harry are the same character and Enemy Of The State is a stealth sequel to The Conversation.
Surprisingly, Enemy Of The State offers up a wealth of evidence. Brill's N.S.A. file features a photo of Hackman from The Conversation, while Brill wears the same type of raincoat from the 1974 film. Brill's work station is almost identical to Harry's and he ends up destroying it again - this time via explosion when the N.S.A raid his warehouse. Brill's real-name is said to be Edward Lyle, which could just be an assumed name.
While there's evidence Brill and Harry could be the same person, it's more likely Tony Scott was a big fan of The Conversation, so once Hackman was cast he wanted to pay homage. The tones of the two movies are quite different as is Brill's personality, but that said, it's up to viewers. There are also theories supporting the idea Sean Connery's John Mason from The Rock is really an older version of his James Bond, which is how some fans view the movie. Imagining Enemy Of The State's Brill is a more bitter, gruffer version of Harry makes his character even richer, so its a theory worth examining.