Carbon is an element which shows the oxidation state of 4 which combined with its property of catenation, makes it possible to form a huge number of compounds.

Catenation is the property by which it can make bonds with other carbon atoms to form long chains.

Hence, carbon, with the least diffuse valence shell p orbital is capable of forming longer p-p sigma bonded chains of atoms than heavier elements which bond via higher valence shell orbitals.

This means that the catenation property shown by carbon is more profound than any other element like silicon.

So due to this property carbon can form millions of compounds. There are more compounds of carbon than every other element put together.