Gunnar Nordstrom was a Finnish theoretical physicist. Nordstrom was the first to formulate a theory of gravity in 5 dimensions, to describe both electromagnetism and gravity in 4 dimensions. The theory, however, is not well known, as it had to compete with general relativity. Nordstrom's theory was too primitive to include both Einstein's and Maxwell's field equations. Despite this, he is considered by many writers as the "Einstein of Finland". He is also considered to have been an early rival of Einstein.
Believe it or not, Nordstrom's theory of gravity was put forth before general relativity was even published. His idea was to produce a 5-dimensional Maxwell theory to unify electromagnetism with gravity. Nordstrom's theory correctly described Maxwell's field in 4 dimensions. However, the theory was a scalar theory of gravity, which is known to be incorrect. It was too primitive to describe both the Einstein and Maxwell fields. Nordstrom's ideas were largely forgotten. He may have been before his time, as he published his theory 1 year before Einstein published general relativity. That being said, he couldn't properly produce a 5-dimensional theory of gravity, as it was described by Albert Einstein.