Citron (Lemon) is one of the most known czech rock/heavy metal groups of 70s and 80s. The group was founded in 1976 by experienced musicians Aleš Ulm, Olda Říha, Tolja Kohout from Katapult and Petr Michalík. They have recorded many singles and albums and although they split a few times, they're still playing. They have sold more than one million of record over the time, from that more than half a million were Plni energie (sold as Full of Energy at the western Europe) and Radegast.