A multi-enzyme complex that catalyzes the oxidative decarboxylation of alpha-ketoglutarate (also known as 2-oxoglutarate) to form succinyl-CoA. The complex comprises multiple copies of three enzymes referred to as E1, E2 and E3: oxoglutarate dehydrogenase (lipoamide) (E1), dihydrolipoamide S-succinyltransferase (E2) and dihydrolipoamide dehydrogenase (E3). Additional proteins may also be present.