Complex sentence: Eduard Lassen (13 April 1830--15 January 1904) was a Belgian composer and conductor of Danish birth who spent most of his career working as the music director at the court in Weimar.
Split into simpler sentences: Eduard Lassen (13 April 1830--15 January 1904) was a Belgian-Denmark-Danish composer and conductor. Although of Danish birth, he spent most of his career working as the music director at the court in Weimar.