ALBANY — After 85 years, a downtown insurance firm is trading its independence for growth opportunities with the help of the world’s fourth largest insurance brokerage and risk management firm.

Fuller & O’Brien announced Thursday it is merging with Arthur J. Gallagher & Co. The deal marks Itasca, Ill.-based Gallagher’s entrance into the Capital Region. It also promises to strengthen Fuller in its core construction industry business, which includes products for commercial property and casualty, workers’ compensation, surety bonding and risk management services.

Fuller President Thomas Tyrrell will become the area president for Gallagher’s Northeast retail property/casualty brokerage arm. Fuller will retain its name along with its 25 workers and office on Broadway.

Tyrrell said the decision to merge was not prompted by Wall Street’s tumult. It is “our finding a way to best ensure the perpetuation and continued growth of the company.” Since January, Gallagher has acquired over 20 other firms worldwide.