Perhaps Marx' significance in the history of economics can be
described more accurately by giving the defining characteristics of
his thought. For instance:

Karl Marx (May 5, 1818 -­ March 14, 1883) was a philosopher whose
project was the construction of a system of Practical Philosophy the
foundation of which was Political Economy. Marx constructed his system
by the critical revision of the Economic Thought previous to him from
the standpoint of Hegelian Dialectics. His system of Political Economy
can thus be labeled "Dialectical Economics". Marx is the most widely
cited thinker of the Hegelian tradition in Economics. His ideas have
inspired many to advocate for revolutionary political change. His
writings include Das Kapital (1867), Economic and Philosophical
Manuscripts of 1844(1932), and Manifesto of the Communist Party (with
Friedrich Engels)(1848).

Hope this helps.

Best regards,

Kepa Ormazabal