Lex Luthor is the main antagonist of Superman & Lois, serving as an unseen antagonist in Season 1, the overarching antagonist of Season 3 and will return in some capacity in Season 4.
He is the arch-enemy of Clark Kent and Lois Lane who sought revenge on them by creating Doomsday, a being capable of killing Superman.
Smallville Citizens:Sarah Cushing, Kyle Cushing, Sophie Cushing, Sean Smith, Timmy Ryan, Tag Harris, Tegan Wichem, Candice Pergande, George Dean Metropolis: Perry White, Ron Troupe, Dabney Donovan, Oliver, John Diggle, Jimmy Cutter
Criminals: Intergang (Thaddeus Killgrave, Bruno Mannheim, Onomatopeia), Inverse Society (Ally Allston, Lucy Lane), Atom-Man, Nuclear Man U.S. Military: General Hardcastle, Mitch Anderson, Reno Rosetti, Jason Trask, Supermen of America John Henry Irons' Earth:Kal-El/Superman, General Sam Lane, Lois Lane, Tal-Rho Bizarro World: Kal-El, Ally Allston, Lois Lane, Jonathan-El, Jordan-El, Lana-Rho, Bizarro Tal-Rho Kryptonians:Leslie Larr, The Eradicator, Zeta-Rho, General Zod Earth-38:Clark Kent/Superman! (Earth-38), Lois Lane