Andy Rubin, the creator of Android and a key executive at Google Inc. for nine years, left the company in 2014 shortly after an internal investigation determined that he had carried on an inappropriate relationship with a subordinate, The Information has learned.

Mr. Rubin has taken a leave of absence from his new smartphone startup, Essential, for personal reasons, the firm’s employees were told on Monday. The Information had earlier contacted Mr. Rubin’s spokesman for this story.

Google initiated its investigation after an employee complained to the company’s human resources division about her relationship with Mr. Rubin, according to three people familiar with the matter. The people declined to elaborate on the specific nature of the woman’s complaint against Mr. Rubin.