Complex sentence: William H. Bell was an African-American servant of William Seward, who is most known for being the servant who greeted William Seward's assassin the night of April 14th, 1865 and for giving testimony against Lewis Powell during the Abraham Lincoln military tribunal.
Split into simpler sentences: William H. Bell was an African-American servant of William Seward, and is best known for his role in greeting Seward's attempted assassin and his testimony in the Lewis Powell trial. He is most known for being the servant who greeted William Seward's assassin the night of April 14th, 1865 and for giving testimony against Lewis Powell during the Abraham Lincoln military tribunal.