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Friday, Apr 10, 2026

OC500 2025: GREG ZIMMER 

GREG ZIMMER 

CEO 

ALLIANT INSURANCE SERVICES INC. 

 

WHY: 30-year finance exec running world’s fifth largest insurance broker, with companywide revenue surpassing $5B in 2024, up 30% y/y.  

IN THE NEWS: Retains title of largest insurance brokerage in OC, reporting revenue climbed 21% to $459M in 2024.  

NOTABLE: Joined Alliant in 1998 as CFO and became president in 2007, where he engineered firm’s explosive growth by overseeing the acquisition of more than 100 companies. Named CEO of Alliant in 2024, taking over for Tom Corbett, who became executive chairman.  

QUOTABLE: The property and casualty marketplace has moderated from prior years, which “has served as a benefit to clients with low claims activity.” 

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