Complicated:

Edward Cooper owned the observatory where the discovery was made, at Markree Castle. Again, we are talking about a gifted amateur of considerable ability and devotion.

His assistant, Andrew Graham, made the actual discovery on April 24, 1848, and was duly was given the choice of name - It was he who decided, but he did so on suggestion by others: Romney Robinson , head of the Armagh observatory,suggested Metis, while John Herschel suggested Thetis.

So I guess the answer is Romney Robinson.

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