They were completely separate corporate entities. Lear was an aviation electronics company and Bill Lear wanted it to become an aircraft company but the board would not agree.
Bill Lear then sold his interest in Lear the aviation electronics company to Siegler, which had started as an HVAC company but had expanded into other areas including electronics, and the two merged giving Lear Siegler. The management of the new merged company was almost all from Siegler.
Bill Lear then sold his interest in Lear the aviation electronics company to Siegler, which had started as an HVAC company but had expanded into other areas including electronics, and the two merged giving Lear Siegler. The management of the new merged company was almost all from Siegler.
Bill Lear then started Lear the aircraft company.