Ravana's father was a Brahmin while his mother a Rakshasi. Then why is he considered a Rakshasa, Rather than a Brahmin. Is it because of his actions?
In the famous dialogue between Yama (in form of Yaksha) and King Yudhishthira there is mention about the eligibility to be a a brahmin. The verse goes as follows(Question no-31):
The Yaksha asked,—“By what, O king, birth, behaviour, study, or learning both a person become a Brahmana? Tell us with certitude!”
Yudhishthira answered,-“Listen, O Yaksha! It is neither birth, nor study, nor learning, that is the cause of Brahmanahood, without doubt, it is behaviour that constitutes it. One’s behaviour should always be well-guarded, especially by a Brahmana. He who maintains his conduct unimpaired, is never impaired himself. Professors and pupils, in fact, all who study the scriptures, if addicted to wicked habits, are to be regarded as illiterate wretches. He only is learned who performes his religious duties. Even if he has studied the four Vedas is to be regarded as a wicked wretch scarcely distinguishable from a Sudra if his conduct be not correct. He only who performes the Agnihotra and has his senses under control, is called a Brahmana!”
Thus it is quiet evident that caste is just a function of a character. Incase of Ravana he failed to keep his sense under control and never behaved like a Brahmana.Thus Ravana doesn't inhert the caste of his father.
- Because Vishrava (Ravana's father) cursed Kaikashi (Ravana's mother):
O thou having the gait of a mad elephant, there reigns a powerful desire in thee for having ofspring. Inasmuch as thou hast come to me at this fierce hour, hearken, thou amiable one, as to the kind of ofspring that thou shalt bring forth. Thou shalt, O thou of graceful hips, bring forth terrible and grim visaged Rakshasas delighting in frightful friends, and of cruel deeds.
Hearing his speech, she, bowing down, said, O reverend (ascetic), such sons of terrific ways seek I not from thee that followest the Veda. Therefore it behoveth thee to favor me. On being thus besought by the girl, Visrava, best of ascetics, again addressed Kaikasi, like the full Moon addressing Rohini, O fair faced one, the son that thou bringest forth last, shall be like unto my line, he shall, without doubt be righteous souled.
Having been thus accosted, the girl, O Rama, after a length of time brought forth a very terrible and hideous ofspring having the form of a Raksha (Rakshasa).
His mother was from Rakshasas (his mother Kaikashi was daughter of Rakshasa Sumali)
He joined his maternal grandfathers/uncles who were from Rakshasas and became king of Rakshasas (this is discussed here).
A Brahmana is not Brahmana by birth alone. He, it is said by the wise, in whom are seen those virtues is a Brahmana. And people term him otherwise in whom those qualities do not exist, even though he be a Brahmana by birth. (Source: Vana Parva: Tirtha-yatra Parva of Mahabharata)