He's an obscure figure to non-Italians, but Diego Martelli (1838-1896) was an important art critic who championed the pre-Impressionist Macchiaioli group. Some of them, in turn, favored him by painting his portrait.
Below are examples.
Gallery
Boldini gained fame for his flashy society portraits made after leaving Italy for Paris. The painting above is basically a small sketch that can be seen in Florence's Pitti Palace.
Fattori painted Martelli and his wife (in a separate work) while at Castiglioncello, a seaside town popular with some of the Macchiaioli.
This too is in the Pitti collection.
Degas had family connections in Italy and also found time to portray Martelli.
I find it interesting to see how different artists portray the same subject. In the case of Martelli, there could be a little disagreement regarding his nose, and his hair color also varies (it seems brown in the earlier two portraits; might he have dyed it black a few years later?).