Between 1915 and 1924, Conlin, under the stage name "Alexander, The Man Who Knows," was a popular and highly paid stage mentalist.

According to one of Conlin's biographers, David Charvet, Alexander was the son of Berthold Michael James Conlin. Within the family Claude Alexander was known as "C. A." and his brother Clarence B. Conlin was known as "C. B." Clarence B. had a successful career as an attorney and he also worked as a stage mentalist, although his fame never equalled that of Claude Alexander. Clarence's granddaughter, Cathy Stevenson, inherited scrap book material on the careers of both her grandfather "C. B." and great-uncle "C. A.", which allowed biographers to take a closer look at the life of Alexander the Crystal Seer, whose activities had long been shrouded in mystery.

Both Charvet, writing in the 2000s, and one of Alexander's publishers of the 1940s, Robert A. Nelson, have said that Alexander was the highest-paid mentalist in the world at the height of his career, during the 1920s. Both sources state that he earned multiple millions of dollars during his career on stage and that during his lifetime he may have been the highest paid entertainer in the field of magic.

Charvet, who interviewed surviving members of Alexander's family, says that Alexander had "seven marriages (sometimes to more than one woman at once), [spent] time [...] in local jails and federal prison, [went on] trial for attempting to extort an oilman millionaire, [made a] failed attempt to out run the authorities in a high powered speed-boat loaded with bootlegged liquor, and [...] admitted killing four men."

Another biographer, Darryl Beckmann, wrote that Alexander was "married eleven times" and was a "con-man" as well as a stage performer.

Alexander promoted his psychic act as a form of mental telepathy or mind reading. Audience members gave him sealed questions, which he answered from the stage. With respect to the question of psychic phenomena, magic, spiritualism, and the occult, Alexander led a sort of double life.

On the one hand, in 1921 he wrote and published The Life And Mysteries Of The Celebrated Dr. Q (also known as The Dr. Q. Book), which was later re-published by Nelson Enterprises of Columbus, Ohio for the stage magic trade. In this book, Alexander exposed the techniques used by fraudulent spiritualist mediums to dupe their clients, provided blueprints for the manufacture of psychic act stage props, and even revealed the famous "Zancig Code" pioneered by the mentalists Julius and Agnes Zancig.

On the other hand, like the Zancigs, he never completely discounted the possibility that spiritualism might contain elements of truth, and he also operated a publishing house, the C. Alexander Publishing Company in Los Angeles, California, which released his own pro-spiritualist and New Thought material, including a multi-volume series called The Inner Secrets of Psychology and a booklet for his clients called Personal Lessons, Codes, and Instructions for Members of the Crystal Silence League. The back cover of the latter volume displays Alexander's connection to the New Thought movement, for it lists an extensive array of titles that Alexander offered for sale, including works written and published by the New Thought author William Walker Atkinson under his own name and also under the pseudonyms Theron Q. Dumont, Yogi Ramacharaka, and Swami Panchadasi; as well as a book by Atkinson's sometime co-author, the occultist L. W. de Laurence.