Born into an average middle-class family, Guilliman has lived a comfortable life. His father Connor, a lawyer, has a strong enthusiasm for boxing and martial arts films, a trait Robert inherited from spending time with him as a child - he cites Bloodsport and Kickboxer as the ones they would always watch. As such, he began training in kickboxing from an early age under Kyokushin Karate master Takashi Kurita, in the Los Angeles based Kurita Kyokushin Dojo. He attended Arcadia High School, where he played football as a quarterback. After high school, he attended Cal State LA, earning All-American honors when playing for the Golden Eagles. He graduated with a bachelor’s degree in Business Administration. With the rise of MMA in the turn of the millennium, Robert found his calling as a mixed martial artist, taking up Brazilian Jiu-Jitsu under Davion Teixeira, of Teixeira Jiu-Jitsu, to complement his striking skills. His MMA career started in 2007 at the age of 21, where he would defeat Aurelio “El Dorado” Logroño in Portland, Oregon. He would later win three more fights against Roger “The Praetorian” Dornier, Fulton “Phoenix” Grimm and “The Red Angel” Angelo O’Shea, before receiving his first loss at the hands of Russell “The Executioner” Leman via knockout, which also resulted in a broken orbital bone around his left eye. It would take him some time to heal before returning to action, but he would avenge this loss the following year, defeating Leman via KO after a roundhouse kick to Leman’s head resulted in a broken jawbone. The following years saw Guilliman win against Röderyk Magnussen, Ian “The Plague” Marton and Mongolian Muay Thai fighter Batsaikhan “The Khan” Jaghatai, before being submitted in 2017 by “The Lion” Lionel Johnson. After recuperating and going through training camp one more time, he would one more time avenge his defeat a year later, defeating Johnson via split decision. It was then that Guilliman attracted the attention of Real Killas MMA, beginning to work in a new training program, after making it through a tryout, before he made his way into the current MMA circuit.