Historical clue formulations

• Clark Kent has one — 2026-06-11
• This isn't who you really are — 2024-06-13
• Second half? — 2023-10-20
• The other you — 2022-10-02
• Spider-Man, for Peter Parker — 2020-03-24
• Second person? — 2019-05-09
• Norman Bates or his mother, in "Psycho" — 2019-03-14
• Secondary identity ... or what can be found in 18-, 27-, 40-, 54- and 66-Across — 2018-11-06
• Hannah Montana, for one — 2018-10-20
• Bosom buddy — 2017-06-24
• You again? — 2015-10-02
• Doppelgänger — 2010-08-26
• Captain Marvel, to Billy Batson — 2009-05-15
• Tony Clifton, to comic Andy Kaufman — 2005-12-11
• Holmes to Conan Doyle, e.g. — 2005-11-03
• Trusted friend — 2003-03-14
• Mr. Hyde, to Dr. Jekyll — 2002-04-02
• Perfect substitute — 2001-07-13
• Trusted friend — 2001-03-18
• Substitute — 2000-04-22
• Bruce Wayne, to Batman — 1998-11-05
• Hyde, to Jekyll — 1998-09-19
• Clark Kent, for one — 1998-05-09
• Mr. Hyde, e.g. — 1997-07-27
• Sidekick — 1997-01-22
• Inseparable friend — 1994-10-27
• Second self — 1993-11-26