This is how the Oxford English Dictionary defines celebrity (the other entries are not relevant to people). I would argue these definitions apply very well to Mandela. Unfortunately, because the word is applied so regularly to people such as the Biebers and Hiltons of the world, our understanding of the word has changed perhaps.
3. The condition of being much extolled or talked about; famousness, notoriety.
a1600 R. Hooker Of Lawes Eccl. Politie vii. viii, in Wks. (1662) 22 The dignity and celebrity of‥Mother-cities should be respected.
1751 Johnson Rambler No. 165. ⁋6, I did not find myself yet enriched in proportion to my celebrity.
1838 T. Arnold Hist. Rome I. 332 Recommended to public notice by the celebrity of their family.
1863 M. Arnold in Macmillan’s Mag. 7 Jan. 255 They [Spinoza’s successors] had celebrity, Spinoza has fame.
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4. concr. A person of celebrity; a celebrated person: a public character.
1849 D. M. Mulock Ogilvies ii, Did you see any of those ‘celebrities,’ as you call them?
1856 R. W. Emerson Eng. Traits xi. 195 One of the celebrities of wealth and fashion, confessed‥that [etc.].
1876 C. M. Davies Unorthodox London 99 Thronged with the spiritual celebrities of London.