In alchemy, Calid often refers to a historical figure, Khalid ibn Yazid (died 704 CE). He was an Umayyad prince, a brother of Muawiyah II who was briefly caliph. Prince Khalid lost the chance of inheriting the title, but took an interest in the study of alchemy, in Egypt, facilitating translations into Arabic of the existing literature. It is to this Khalid that later allusions to Calid rex (King Calid) refer.
It is contested whether the attributions to Khalid ibn Yazid of alchemical writing are justified. A popular legend has him consulting a Byzantine monk Marianos (Morienus the Greek). The Liber de compositione alchimiae, which was the first alchemical work translated from Arabic to Latin was purportedly an epistle of Marianos to Khalid.
Another traditional attribution is of the Liber Trium Verborum. Forms as Calid filius Ysidri attempt to distinguish ibn Yazid from others named Calid. Calid filius Hahmil certainly intends ibn Umail. There is a Calid filius Jaici mentioned by Jean-Jacques Manget, who includes an attributed Liber Secretorum Artis in his 1702 compilation Bibliotheca Curiosa Chemica.