Bengal
Bengal (Duc No Tranh) is an interesting Marvel character in my view who has been portrayed as both a hero and a villain. He first appeared in Daredevil, when he traveled to America to seek vengeance as an adult on soldiers who were involved in the destruction of his village during the Vietnam War. Bengal could be an interesting Asian character for the show, and a tough challenge for Luke Cage. Daredevil has already had a strong Asian influence, and we can expect to see an even greater Asian influence within the Netflix Marvel universe when Iron Fist debuts next year. The Vietnam War aspect of Bengal's backstory is also something that could be explored. Jessica Jones and Daredevil both had subplots that related to secret military programs and past war conflicts during their separate series - one involving Nuke (Officer Frank Simpson) on Jessica Jones and one involving The Punisher in Daredevil Season Two. Such a story could work for Luke Cage as well.
John Bushmaster
John Bushmaster (John McIver) would also be quite a match up for Luke Cage. Bushmaster, who is of Caribbean descent, started out as a low-level criminal who rose through the ranks to become a powerful crime boss. He has had clashes with Luke Cage in the comics, and even once kidnapped the nurse Claire Temple - who will be a supporting character on Luke Cage this season after previously appearing on Daredevil and Jessica Jones. What also makes him an interesting match for Cage is that Bushmaster was physically augmented in the same way as Luke Cage - that is something that could be addressed on the series. Are there others like Luke Cage out there? Bushmaster could be used to help answer that question. He also has a younger brother that took on the name Bushmaster at a later time.
Hardcore
Hardcore (real name unknown) is another super villain with a Caribbean background - he is from the U.S. Virgin Islands. Hardcore is a mercenary and skilled combatant in Japanese weaponry. In addition to his formidable fighting ability and weapons skills, Hardcore also has some physical enhancements to his fingernails that allows him to slash through even the strongest metals. He is another character that I could see featured on Luke Cage, Daredevil, Jessica Jones, or Iron Fist. His island background would fit in well with the diversity of Harlem, and his comic book affiliation with one of the Bushmaster brothers and conflicts with Luke Cage would also make him a good fit for the series.
Glowworm
Glowworm (William Blake) is another Luke Cage villain who was experimented on - though in his case he actually volunteered. As a marine, he was involved in attempts to recreate the formula that produced Captain America in the Marvel Universe. Instead of creating another Steve Rogers, the experimentation led to him becoming a glowing white super villain with a self-hatred towards other African-Americans. This was due (in his words) to his growing up in the 'Deep South' and experiencing rampant racism first hand. He convinced himself of the belief that blacks were inferior. Glowworm is a bit of a bizarre yet interesting character to explore in the series for many reasons. One is due to the many definitions of what it means to be 'black' in 2016 - socially, culturally, and politically. Is being black color or culture? Another angle could explore the deeper meanings behind the character on Luke Cage. Blake was a black man who appeared 'white' when he attacked others of his race. It wasn't until he was defeated by Cage that his true identity was discovered.
Moses Magnum
Moses Magnum (his real name) would be a very difficult challenge for Luke Cage. Magnum is an Ethiopian-American who emigrated from his home country and became the leader of an independent weapons manufacturing firm. In his comic book backstory, his family sided with Mussolini during Italy's invasion of the country prior to World War II, which forced them to flee to the United States. That backstory could be easily updated to include modern day terrorist groups in Africa like Al-Shabab, ISIS, or Boko Haram - or he could be portrayed as a second or third generation immigrant and maintain the Mussolini-Ethiopia connection. Magnum would also be a great choice for a major villain for an entire series, with his interesting backstory and immense wealth as a corporate leader. He is very reminiscent of an evil version of Tony Stark, the alter ego of Iron Man. Magnum also later developed superhuman abilities through experimentation in the comics, so he could be portrayed several different ways on Luke Cage for added flexibility.
A Bonus Villain For the People - Coldfire