Complex sentence: The eldest great-grandson of Count Aleksey Alekseyevich was Count Aleksey Aleksandrovich Bobrinskoy (1852-1927), who led the Council of United Nobility since 1906 and represented the nobility of the St Petersburg guberniya in the Senate and the 3rd State Duma.
Split into simpler sentences: The eldest great-grandson of Count Aleksey Alekseyevich was Count Aleksey Aleksandrovich Bobrinskoy (1852-1927), who led the Council of United Nobility beginning 1906. He represented the nobility of the St Petersburg guberniya in the Senate and the 3rd State Duma.