Field Marshall Frederick Roberts, 1st Earl Roberts.

Roberts was appointed Commander-In-Chief of the Forces on 3rd January 1901, this image must have been taken shortly afterwards as it is one of Stuart's earlier Hudson & Kearns cards, as are most of his military subjects.

I would love to know the location of this card, it seems to be one of a series, perhaps taken on the same day, that Stuart published.

See this Wikipedia entry for further details.