This thesis presents a search for a heavy Higgs-like resonance decaying in the R→WW∗→ℓνℓν channel using the ATLAS detector at the Large Hadron Collider. The search uses proton-proton collision data at a centre-of-mass energy of 13 TeV corresponding to an integrated luminosity of 139 fb−1. Interpretations are given under the narrow-width approximation, Georgi-Machacek model, the radion particle of the Randall-Sundrum graviton model, a HVT model, and a spin-2 graviton of the Randall-Sundrum model.