From Longman Dictionary of Contemporary Englishbe a (great/firm) believer in somethingbe a (great/firm) believer in somethingAPPROVEto believe strongly that something is good and effective I’m a great believer in regular exercise. → believer
Examples from the Corpus
be a (great/firm) believer in something• Daley was a firm believer in the bootstrap theory.• He was a firm believer in the power of prayer.• He was a great believer in expressing aggression, not bottling it up.• Lampard was a great believer in eating whenever you could.• Letterman is a believer in the immigrant mentality.• Molly was a believer in homeopathy and underwent her last operation and subsequent treatment in the Royal London Homeopathic Hospital.• She is a believer in fundamentals, in technique.• Tip is a firm believer in fate, and in 1961 the finger pointed in the right direction for him. 