May I call Samuel Johnson a PhD? According to Wikipedia, Samuel Johnson


  was awarded an honorary doctorate in 1765 by Trinity College Dublin and in 1775 by Oxford University.


Also, apparently people referred to him as "Dr Johnson" back then.

May I put "PhD" after his name now, for example, in a caption?  Like this?


  Samuel Johnson, PhD (1709–1784)
No. 

He was an LL D of Trinity College, granted 1765; and a DCL of Oxford, granted 1775.

See https://www.britannica.com/biography/Samuel-Johnson

Note: 
DCL= Doctor of Civil Law.
LL.D.= Doctor of Laws, that is of both the Civil and the Canon Law.