Hans Christian Cornelius Mortensen (27 August 1856 – 7 June 1921) was a Danish teacher and ornithologist.

In 1891, he married Ingeborg Lemming (1858-1938), a fellow teacher and feminist who assisted him with his bird ringing.

Mortensen's first successful experiments with bird ringing took place in 1899 with common starlings.

He made most of his bird rings himself, cutting them from aluminium sheet and stamping each with an address and an individual number.

In 1906, he was a co-founder, with Eiler Lehn Schiøler, of the Danish Ornithological Society.