Lady Sylvia Olive Pleadwell Sayer (1904-2000) was one of the foremost early conservators of what is now Dartmoor National Park, in Devon in the south-west of England. She was ennobled in 1959 when her husband, Vice-Admiral Guy Sayer was knighted as the Flag Officer Commanding Reserve Fleet.

Despite Lady Sayer's establishment background, she was a fearless and empassioned fighter in the defence of Dartmoor: frequently she deliberately interrupted army live-firing exercises on Dartmoor's military ranges, and in 1985 snubbed The Prince of Wales over the Duchy of Cornwall's management plan for Dartmoor, since this allowed for a continuance of military usage.