Robert S. Horn was born in Tulsa, Oklahoma on May 13, 1979. He graduated from Bishop Kelley High School in June of 1998. 
 
Private Horn enlisted in the Marine Corps on October 12, 1999. Upon completing recruit training at MCRD San Diego, Pvt Horn was promoted meritoriously to the rank of Private First Class. Following recruit training, PFC Horn attended Marine Combat Training (MCT) Camp Pendleton, California. Upon completion, he was sent to Fort Leonard Wood, Missouri to attend Motor Transportation School. 
 
After completion of Motor Transportation School, PFC Horn received the Military Occupation Skill (MOS) 3531 Motor Transportation Operator and reported to Marine Wing Support Squadron 372 at Camp Pendleton, California on May 2000. PFC Horn was promoted to Lance Corporal January 2001 while serving as a Motor Transportation Operator. 
 
LCpl Horn Played baseball for the All Marine Baseball Team while stationed at Camp Pendleton, California. LCpl Horn was promoted to the rank of Corporal in December 2002 while still at Marine Wing Support Squadron 372. Cpl Horn deployed with MWSS 372 to Iraq in support of Operation Enduring Freedom in January 2003. Upon return from Iraq, Cpl Horn separated from the Marine Corps in October 2003 to further his education and play baseball in college.  
 
Cpl Horn decided to return to the Marine Corps in November of 2006. While at the recruiting station in Tulsa, Oklahoma Cpl Horn received orders to 1st Battalion, 7th Marines, Twenty-nine Palms, California in March 2007. Cpl Horn deployed to Camp Hiit, Iraq for Operation Iraqi Freedom with 1/7 as a Motor Transportation Operator 3531. 
 
Cpl Horn was promoted to Sergeant in January 2008 while deployed with 1/7 at Camp Hiit, Iraq. Sgt Horn lateral moved into the MOS 6314 Aviation Technician. Upon the return from deployment with 1/7 Sgt Horn received orders to Pensacola, Florida for Avionics Technician School. After graduating Aviation Technician School, Sgt Horn received orders to VMU-1 Unmanned Ariel Vehicles in Twenty-nine Palms, California. Sgt Horn was promoted to the rank of Staff Sergeant in July 2010 while serving as the platoon sergeant for the Maintenance shop at VMU-1.
 
 In September 2010, SSgt Horn received orders to VMU-4 in Yuma, Arizona to be the Maintenance Control Chief. While at VMU-4, SSgt Horn was HSST for Drill Instructor Duty August 2012. 
 
In April 2013, SSgt Horn reported to Drill Instructor School at Marine Corps Recruit Depot San Diego, California. After completing Drill Instructor School, SSgt Horn was assigned to 2nd Bn, Hotel Company.  SSgt Horn Was promoted to the rank of Gunnery Sergeant May 2014 while serving as a Drill Instructor. GySgt Horn served as Drill Instructor, Senior Drill Instructor, and Chief Drill Instructor of Hotel Company. 
 
August 2016, GySgt Horn received orders to Wounded Warrior Battalion East Bethesda, MD. While at WWBN-E, GySgt Horn served as Marine Corps Liaison and Section Leader of the wounded, ill, and injured. 
 
December 2017, GySgt Horn was selected to the rank of First Sergeant. GySgt Horn was Frocked to First Sergeant and received orders to 3d Battalion 5th Marines at Camp Pendleton, California where he became the Kilo Company First Sergeant. As the Kilo Company First Sergeant he deployed with the Battalion Landing Team 3/5 with the 11th Marine Expeditionary Unit 19.2. Upon completion of the 11th MEU 1stSgt Horn deployed to the Southwest Border Mission San Diego, California as the India Company 1stSgt. While at the Border Mission 1stSgt Horn received orders to 1st Reconnaissance Battalion.
 
 July 2020 1stSgt Horn reported to 1st Reconnaissance Battalion to be the Alpha Company 1stSgt. April 2021 while at 1st Reconnaissance Battalion 1stSgt Horn was moved to be the Force Reconnaissance Company 1stSgt. November 2021 1stSgt Horn was selected to the rank of Sergeant Major and has orders to Heavy Helicopter Squadron 361, Marine Air Group 16, 3d Marine Air Wing. 

On January 11, 2024, SgtMaj Horn took over as the Sergeant Major of Marine Aviation Logistics Squadron 11, Marine Aircraft Group 11, 3d Marine Air Wing. 
 
Sergeant Major Horn's personal awards include (2) Navy and Marine Corps Commendation Medals, (2) Navy and Marine Corps Achievement Medals.