One of the best known names in gambling, Caesars Entertainment, has agreed to bought by Eldorado Resorts in a deal worth $17.3bn (£13.6bn).
It will create one of the largest casino firms in the US, and comes after a few turbulent years for Caesars.
Caesars owns 34 casinos including Las Vegas-based Caesars Palace, which has hosted major sports and music events.
The company was in financial trouble for a decade and emerged from bankruptcy in 2017.
Eldorado will buy Caesars for about $8.5bn in cash and shares and also take on the firm's huge debt. It is part of a plan to compete with major competitors such as Las Vegas Sands and Wynn Resorts.
Billionaire activist investor Carl Icahn built a 14.75% stake in Caesars and urged the company to put itself up for sale as a way to cut debt.
Three months ago Caesars agreed to give Mr Icahn's investment business three board seats and a say on the selection of its next chief executive.
Mr Icahn said he was "pleased" by the deal, adding in a statement: "It is rare that you see a merger where, because of the great synergies, 'one plus one equals five'. I look forward to seeing our investment prosper."
Caesars operates casinos with the Harrah's and Horseshoe brands. Eldorado owns 26 properties in 12 US states. The combined company will retain the Caesars name and own, operate and manage 60 casino-resorts across 16 states.
The most famous property in Caesars' portfolio is the luxury hotel and casino Caesars Palace, created in 1966 with an interior designed to resemble the opulence of the Roman Empire.
Frank Sinatra was a regular performer, Muhammad Ali boxed there, and the car park hosted Formula One races in the early 1980s.
In a parallel deal also announced on Monday, the combined company will sell some of its property estate to Vici Properties to help pay down debt.
Eldorado has expanded rapidly through acquisition and has seen its share price climb more than 12-fold in the past five years.