Brian Russell and Richard McConnell created the Clipper language. Clipper started out as nothing more than a DbaseIII+ compiler and grew to be so much more. Brian (along with Richard McConnell) introduced many concepts from Smalltalk and the SelfLanguage into the Xbase community through Clipper. As a result, Nantucket (the company that owned Clipper) introduced and evangelized ObjectOrientation to great hoards of people. These included lexical-closures (styled after Smalltalk blocks), classes, a Generational and Incremental Scavenging Garbage Collector, a language neutral extend-system, Replaceable Database Drivers (RDD's), and much more that was usurped after Nantucket was purchased (and put to bed) by Computer Associates.
Brian always maintained that he wanted Clipper to subversive. It is no surprise that when Xbase finally started to die out, many (self-proclaimed) Clipper-heads ended up becoming Smalltalk programmers or working in a pure ObjectOriented language. Brian has often stated that the overriding goal in anything he did was to subvert the dominant paradigm. Luckily his software was not quite as nihlistic as his aesthetic!
In addition to the great technical achievements one would not normally associate with Dbase, the company itself (Nantucket) created a singular working environment for its developers that was always technology (rather than marketing) driven, inclusive, and rewarded learning and individuality.