Alloys　with　high　yield　strength　and　ductility　are　attractive　for　application　because　of　their　potential　to　offer　mass　reduction,　energy　savings,　and　enhanced　structural　reliability.　However,　increasing　strength　usually　comes　at　the　expense　of　ductility,　which　is　commonly　known　as　the　strength-ductility　trade-off　for　metal　alloys.　In　this　work,　we　explored　a　strategy　of　using　a　heterogeneous　grain　size　structure　and　a　reduced　stacking　fault　energy　in　a　CoCrFeNiMn　FCC　high　entropy　alloy　to　overcome　the　limitations　of　this　trade-off.　By　this　approach,　the　alloy　achieved　a　yield　strength　of　980　MPa,　a　tensile　strength　of　1385　MPa,　and　tensile　elongation　to　failure　of　48%　benefiting　from　cooperative　strain　hardening　via　multiple　mech-anisms,　such　as　hetero-deformation　induced　(HDI)　hardening,　deformation　twinning,　Frank-Read　disloca-tion　sources　and　Lomer-Cottrell　dislocation　locks　instigated　by　such　structures.　These　micromechanisms　of　deformation　help　to　harden　the　alloy　via　in　situ　refinement　of　the　mean　free　paths　for　dislocations.(c)　2022　Acta　Materialia　Inc.　Published　by　Elsevier　Ltd.　All　rights　reserved.