The deal had been on the radar for a few days, but Monday was the day that AT&T announced a merger with Discovery Inc. for $43 billion, the largest deal of 2021 and the third-largest of the 2020s.

The deal would merge all of AT&T's WarnerMedia assets, including properties such as CNN, HBO and Warner Bros, with reality-TV-heavy Discovery, which owns such channels as Food Network and Animal Planet. 

Sullivan & Cromwell; Debevoise & Plimpton; Wachtell, Lipton, Rosen & Katz; and Fried, Frank, Harris, Shriver & Jacobson all had a role in the mega-deal.