Henry Marsh enters insurance brokerage 1871 in Chicago founding Marsh & McLennan precursor. Post-Chicago Fire (Oct 8-10 1871, 17,500 buildings destroyed, $222M damages) brokerage demand surges as commercial fire insurance becomes mandatory for lenders. Cornerstone of modern insurance brokerage.

Donald McLennan founds D.R. McLennan & Co 1905 in Duluth MN; specializes in railroad/lumber industry insurance. McLennan's midwest practice + Henry Marsh's east coast practice merge 1923 forming Marsh & McLennan in Chicago — origin of MMC.

Marsh & McLennan formally merged Mar 1923 in Chicago combining Henry Marsh's east coast practice + Donald McLennan's midwest practice. Becomes largest US insurance broker by 1930; pioneers concept of dedicated risk advisory rather than just product placement.

Marsh & McLennan acquires Sedgwick 1998 for $1.9B + Putnam Investments asset management 1970s + various retirement/benefits firms — builds 'risk + people + capital' platform. Jeff Greenberg (Hank Greenberg's son) leads MMC 1999-2004. Greenberg ousted Oct 2004 over Spitzer bid-rigging probe.

Marsh & McLennan Eliot Spitzer settlement Jan 2005 — pays $850M without admitting wrongdoing after Spitzer's Oct 2004 lawsuit alleging bid-rigging + steering commissions on commercial insurance placements. CEO Jeff Greenberg (son of Hank) resigns Oct 2004. Triggers industry-wide ban on contingent commissions in many states.

Brian Duperreault becomes Marsh CEO Jan 2008 — recruited from ACE; later moves to AIG CEO 2017. Brought stability after Spitzer-era controversies. Predecessor to Dan Glaser (CEO 2013-2022). MMC stock recovers from $20 (2008) to $80 (2014); Duperreault's discipline drives recovery.

Marsh McLennan acquires Jardine Lloyd Thompson (JLT) Apr 2019 for $5.6B all-cash — UK-based specialty insurance broker; largest MMC acquisition. Adds top-5 global insurance + reinsurance brokerage capabilities. CEO Dan Glaser executes acquisition; combined Marsh + JLT becomes #1 global broker by revenue.

John Doyle becomes MMC CEO Jan 2023 succeeding Dan Glaser (CEO 2013-2022). Doyle continues acquisition strategy + tech investment. MMC stock 4x's 2020-2025 from $90 to $230+ as broker fee model proves resilient through hard market + soft market.

John Doyle becomes Marsh McLennan CEO Jan 2023 — succeeds Dan Glaser (CEO 2013-2022). Doyle previously head of Marsh USA. Continues acquisition strategy + tech investment ($1.5B+ over 5 years). MMC reports $24B revenue 2024.

Marsh McLennan announces $7.75B all-cash acquisition of McGriff Insurance Brokers Sep 2024 — closes Nov 2024. McGriff (top-25 US retail commercial broker, $1.5B revenue) bought from Truist Financial as bank divests non-core. Largest broker acquisition since Aon-WTW failed. Combines with Marsh USA.

Marsh McLennan acquires McGriff Insurance Brokers Nov 2024 for $7.75B all-cash — McGriff (top-25 US retail commercial broker, $1.5B revenue) bought from Truist Financial as bank divested non-core. Largest broker acquisition since Aon-WTW failed 2021. Combines with Marsh USA to form $12B+ revenue retail commercial broker.