A sidekick is a slang expression for a close companion or colleague (not necessarily in fiction) who is actually, or generally regarded as, subordinate to the one he accompanies. Some well-known fictional sidekicks are Don Quixote's Sancho Panza, Sherlock Holmes' Doctor Watson, The Lone Ranger's Tonto,  The Green Hornet's Kato, Shrek's Donkey and Batman's Robin.

Borland Sidekick was a personal information manager (PIM) that Borland launched in 1984 under Philippe Kahn's leadership. It was an early and popular terminate and stay resident program (TSR) for DOS operating systems, which enabled computer users to activate the program using a hot key combination (by default:Ctrl-Alt) while working in other programs. Although a text mode program, Sidekick's window-based interface echoed that of the Apple Macintosh and anticipated the eventual look of Microsoft Windows 2.0. It included a personal calendar, text editor (with WordStar-like command interface), calculator, ASCII chart, address book, and phone dialer. According to the prospectus for Borland's initial public offering of stock to the public, Sidekick sold more than 1 million copies in its first three years.