Complex sentence: Johansson suffers from systemic lupus erythematosus, which has caused his face to look swollen and red, giving him the nickname "the leopard" among Gothenburgers.
Split into simpler sentences: Johansson suffers from Systemic lupus erythematosus, this is the reason why his face looks swollen and red. This fact has given him the nickname "the leopard" among Gothenburgers.