1e DMG page 102
"As the DM you are game moderator, judge, jury, and supreme deity. You are also actively engaged in actual role playing throughout the course of the campaign, from game to game,
as you must take the persona of each and every henchman and/or hireling involved. (See also Monsters, here-after.)
To play such roles to the hilt, it is certainly helpful to the DM if he or she has player characters of his or her own in some other campaign."
Of course it also says on page 103
"Some few players will actually play their henchmen as individual characters, not merely as convenient extensions of their main player character. In these rare cases, your involvement with these henchmen will be minimal."
So basically the DM plays them as people unless the player does. Another of the many Gygax contradictions in the DMG.