Sankey diagrams are named after Captain Matthew Henry Phineas Riall Sankey.
Here is some biographical information on Mr. Sankey:
Matthew H. Sankey was an engineer from Ireland. He was born on November 9, 1853 in Nenagh, co. Tipperary (other sources have him being born in Modeshill, co. Tipperary or Bawnmore, co. Cork) to a family of military. His father, William, was a Lieut.-Col. in the 62nd regiment. Sankey joined the military as well and became an engineer in the Corps of Royal Engineers (R.E.) with the rank of a captain.
Later he quit military service and joined Willans works, where he continued to work on the improvement of the efficiency of steam engines.
He became am member of the Institution of Civil Engineers. From 1920 to 1921 he acted as president of the British Institution of Mechanical Engineers. (Read a biography on the IMechE website)
Sankey diagrams are named after him, because he was the first to use them in a publication: In an annex to the minutes for the Institution of Mechanical Engineers in 1898 he sketched the energy efficiency of a steam engine in comparison to an ideal steam engine without energy losses. Sankey diagrams show where material or energy flows with arrows with a width proportional to the flow quantity.
His publications include “The Maps of the Ordnance Survey” (1888), “The Thermal Efficiency of Steam Engines” (1895), “Governing of Steam Engines by Throttling and by Variable Expansion” (1895), “Interim Report of the Committee on tabulating the Results of Steam-Engine and Boiler Trials” (1902) and “The Energy Chart. Practical Applications to Reciprocal Steam-Engines” (1905)
On July 5, 1876 he married Elisabeth Pym, they had
one child four children. Sankey died on October 3, 1925.