Glaurung - Because he was the first of Melkor's dragons, he is often called the "Father of Dragons".  But he was also known at the "Wurm of Morgoth".

"In the front of that fire came Glaurung the golden, father of dragons, in his full might; and in his train were Balrogs, and behind them came the black armies of the Orcs in multitudes such as the Noldor had never before seen or imagined.  And they assaulted the fortresses of the Noldor had never before seen or imagined.  And they assaulted the fortresses of the Noldor, and broke the leaguer about Angband, and slew wherever they found them the Noldor and their allies, Grey-elves and Men." ~The Silmarillion, chap. 18 (Of the Ruin of Beleriand)