Cleary Gottlieb Steen & Hamilton lawyers helped guide Google toward completing the largest acquisition in the company’s history — the $12.5 billion acquisition of mobile-device maker Motorola Mobility Holdings Inc., the firm announced Monday.

In buying the Schaumburg, Ill.-based handset manufacturer, Google — whose Android operating system is used in many Motorola devices — will assume control of one of the mobile industry’s strongest patent portfolios, company executives said.