Valmiki Ramayana Bala Kanda Sarga 25 Shloka 8

अथ thereafter, कस्यचित् कालस्य after some time, यक्षी the female yakshi,Tataka, मारीचं नाम by name Maricha, दुर्धर्षम् unassailable, पुत्रम् son, अजायत gave birth, य: he, शापात् because of the curse, राक्षस: अभवत् became rakshasa.

After some time that yakshini gave birth to an unassailable son by name Maricha. Because of a curse, he became a rakshasa (though born of yaksha parentage).