Warlord Krang is from Atlantis and rose in the ranks of the Atlantean military while Namor was missing, pre-Fantastic Four. Since Namor returned the two have been at odds when it concerns Atlantis. So much that Krang even planned devious schemes through the years to rid Namor from Atlantis. Recently during the Civil War story arc, he was injured by Norman Osborn. Then later would join the Last Defenders.
Krang was later found diseased -- attacking the shores of Russia with a captured Namora. He was banished to another dimension with the help of the Winter Guard and the Agents of Atlas. It is unknown how he returned from the other dimension or recovered from his illness, but he is currently back in Namor's good graces and holding a military position in New Atlantis, beneath Utopia.