Complex sentence: Reno is most noted for his prominent role in the Battle of the Little Bighorn, which has ever since been the subject of controversy regarding his command decisions in the course of one of the most infamous defeats in the history of the United States military.
Split into simpler sentences: Reno is most noted for his prominent role in the Battle of the Little Bighorn. This has since been a subject of controversy regarding his command decisions in the course of one of the most infamous defeats in the history of the United States military.