Valmiki Ramayana Yuddha Kanda Sarga 61 Shloka 12
Original Shlokaप्रकृत्याह्येषतेजस्वीकुम्भकर्णोमहाबलः । अन्येषांराक्षसेन्द्राणांवरदानकृतंबलम् ।।6.61.12।।
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एषः in that way, कुम्भकर्णः Kumbhakarna, प्रकृत्याः by nature, तेजस्वी energetic, महाबलः mighty, अन्येषाम् of others, राक्षसेन्द्राणाम् Rakshasa kings, बलम् strength, वरदानकृतम् is on account of boons.
"Kumbhakarna is by nature (by birth) energetic and mighty. The strength of other Rakshasas is on account of their boons received by them."