Motorola
Motorola is the birthplace of Six Sigma. It was conceived by Bill Smith, an engineer at the company, in 1986.
Many of the concepts within Six Sigma had been around for a while, but this was the first time that they had been organized into a cohesive system for making improvement. And it was quite successful for Motorola. They reportedly saved billions of dollars from their efforts.
While Motorola has lost its place of prominence in the mobile device market, and the luster of Six Sigma has worn off since its heyday, the company had a deep impact on the continuous improvement community that continues to echo to this day.
It is also arguable that both GE and Honeywell were able to use Six Sigma more effectively and were more responsible for its spread, but it is undisputed that Motorola was ground zero for its birth.