William Starke Rosecrans (September 6, 1819 – March 11, 1898) is an inventor, coal-oil company executive, diplomat, politician, and United States Army officer.

He gains fame for his role as a Union general during the American Civil War.

He is the victor at prominent Western Theater battles, but his military career is effectively ended following his disastrous defeat at the Battle of Chickamauga in 1863.

Rosecrans is a graduate of West Point who serves as a professor at the academy and in engineering assignments before leaving the Army to pursue a career in civil engineering.

At the start of the Civil War, leading troops from Ohio, he achieves early combat success in western Virginia.

In 1862 in the Western Theater, he wins the battles of Iuka and Corinth while under the command of Maj. Gen. Ulysses S. Grant.

His brusque, outspoken manner and willingness to quarrel openly with superiors causes a professional rivalry with Grant (as well as with Secretary of War Edwin M. Stanton) that will adversely affect Rosecrans's career.

Given command of the Army of the Cumberland, he fights against Confederate Gen. Braxton Bragg at Stones River, and later outmaneuvers him in the brilliant Tullahoma Campaign, driving the Confederates from Middle Tennessee.

His strategic movements then cause Bragg to abandon the critical city of Chattanooga, but Rosecrans's pursuit of Bragg ends during the bloody Battle of Chickamauga, where his unfortunately worded order mistakenly opens a gap in the Union line and Rosecrans and a third of his army are swept from the field.

Besieged in Chattanooga, Rosecrans is relieved of command by Grant.

Following his humiliating defeat, Rosecrans is reassigned to command the Department of Missouri, where he opposes Price's Raid.

He is briefly considered as a vice presidential running mate for Abraham Lincoln in 1864.

After the war, he serves in diplomatic and appointed political positions and in 1881 is elected to Congress, representing California.