Complex sentence: It was in Jordan's group that he first achieved success playing the Hammond organ and in 1950 he is reputed to have written one of Jordan's biggest hits, "Saturday Night Fish Fry", for which Jordan claimed the writing credit.
Split into simpler sentences: It was in Jordan's group that he first achieved success playing the Hammond organ. In 1950 he is reputed to have written one of Jordan's biggest hits, "Saturday Night Fish Fry", for which Jordan claimed the writing credit.