Conrad Kellogg is an former member of the Shi and an former member of the Institute before he joined the Combines after they conquered Fialer Earth
Born in 2179, Kellogg is originally from the New California Republic on the West Coast. As a child, Kellogg lived in an impoverished household with his abusive father, a former raider, and his loving yet weak-willed mother. Being an alcoholic, Kellogg's father was unreliable as a provider for the family. Instead, Kellogg's mother turned to Conrad for support.
As an adult, Kellogg moved to San Francisco where he married Sarah and had a daughter, Mary. Though Kellogg worked for the Shi, his family was murdered by unspecified assailants - whom he later killed in retaliation.
At some point Kellogg was cybernetically enhanced by the Institute, which halted his aging and extended his lifespan.
After working as a mercenary in Fialer Earth, Kellogg traveled to Zol Earth, where the Combine's Imperial Research Group 975 hired him to find a test subject for a 4th Generation Synth project by the order of the Pure Emperor whom choose the models of Victoria's Secret to be used as candidates (though no-one knows why he did this, it could very well be because of his bizarre sense of humor, which seems to be the most likely reason for many that knows of this odd project). Kellogg chose Behati Prinsloo, and abducted her and turned her as a Synth Super Soldier. Behati's DNA was used by the IRG-975 to complete their Generation 4 synth Super Soldiers.