I have another possible BlackBeard speculation: That BlackBeard is Luffy's blood uncle on his mother's side. It would explain why BlackBeard respects and seem so interested in Luffy. If Luffy's mother's brother was Marshall D. Teach then she would be a Marshall D. as well. Likely she would be attracted to other men with the "will of D." Luffy's mother being Blackbeard's sis would explain why he has a beef with Dragon the guy who knocked up his sister and took her child to give to his father Garp. When you think about it, seem like Garp was hiding Luffy as a child the same way he did Ace which I would elaborate on further. Let's say Blackbeard had a sister, a twin sister who was more infamous than him. For someone like Dragon to love a woman and give her a child, she had to be one remarkable woman/pirate. I have two subtheories I will briefly comment on about the possibility. One theory is Luffy's mother was taken by the World Government and nobles. That would explain why Dragon formed the Revolutionary Army to opposed the World Government. Many men has gone to war over a woman. Let's not forget our good friend Obito. If I had to guess, Dragon was once a respected member of the Navy and was on a fast track to be the next Fleet Admiral. Dragon's world knowledge and militant expertise would support that theory. It's also strange how little is said about Dragon or even done about him. Somehow the World Government got Luffy's mom, maybe by using Dragon as bait. To make the theory even more interesting, let's say Luffy's mom was a crew member on Gol D. Roger's ship. One of the top members, a founding members. She would be above Shanks but below in rank of Rayleigh. What if as a little girl, Luffy's mom gave Gol D. Roger the Straw hat. Let's say that she had a dream of being the Queen of the Pirates, following the death of Roger. She wanted to follow Roger's path again to obtain the One Piece and reveal the truth about the world to all thus becoming Queen of the World! If she made a bold declaration like that she would be the most wanted pirate in the World. Such a bold characteristic is similar to Luffy. Assuming Blackbeard is Luffy's mom's little brother, he would be behind his sister becoming the Queen of the Pirates/Queen of the World. But as I mentioned earlier with this sub theory, that would have been ruined if she was captured by the world Government. To be honest, she could be one of the ancient weapons which would explain why Luffy can somewhat hear voices of sea kings. Perhaps if she was on Roger's ship it would explain why he was able to travel the World seemingly easily. It would explain the cut scene we have seen where Roger heard the voices of the Sea Kings but didn't know where they were coming from. If she was an ancient weapon then she would be able to communicate with them, call them when needed, and they would help guide her which means she likely would have been Roger's navigator. Then if we think about Blackbeard showing up at Impel Down. What if he was not looking for crew members but looking for his sister? I wouldn't put it past Blackbeard to capture Ace to give to the government in order to cause a distraction with the Whitebeard Pirates trying to rescue Ace. Maybe he found his sister in Impel down and absorbed her which is the second sub-theory which user Seriyu has discussed that unique ability. In the opening song for the Dressrosa Arc I thought it was strange that a cut scene came up with Blackbeard asking Luffy to come into the darkness. Of course that is not part of the actual story but it may give us a glimmer of what is Blackbeard's real motives are for Luke, I mean Luffy, which is to join the dark side with Blackbeard and his sister, Luffy's mother. Another small theory is Luffy's mother was killed or believed to be killed in action, maybe fleeing from Dragon or trying to get Luffy back from Dragon. That would explain Blackbeard's beef with Dragon too but if he got her caught by the World Government that would be enough to still piss him off. Garp kept Luffy's mother ID a secret the same reason he kept other's from knowing Dragon was his father because she is likely extremely dangerous. If Luffy's mother was as famous as a pirate as Gold Roger then Luffy's life would have been in danger just like Ace's life was in danger as an infant. If anyone knew that Luffy was related to Blackbeard it would only gain him more enemies and it would made Ace have a slight indifference towards Luffy. Until I see Blackbeard cause real personal harm to Luffy and he definitely can with his powers, I have to believe they are related. In Impel Down, Blackbeard actually helped Luffy. True they did have a small altercation in Impel Down and Blackbeard stated he originally was going to capture Luffy to get his place in the World Government but went with capturing Ace instead, that could have been just a lie to keep Luffy from knowing his real motives and to anger him. Before capturing Ace, Blackbeard told Ace he was going to capture Luffy to give to the government but could have been just to entice Ace to loose his cool making him fight angry not smart and I suspect that the more you fight with anger or darkness, the less effective you are against Teach. Blackbeard would have a vendetta against Ace for his relationship with Whitebeard and being the son of Gold Roger, who if his sister was in his crew, death lead to her unfortunate undoing. If they are related, it is also possible Blackbeard took out White Beard for Luffy. It would explain why Blackbeard thought it was too early for Luffy to call himself a Yonko because the plan was for Blackbeard to allow Luffy to "defeat" him to become a Yonko. Blackbeard didn't become active until he first met Luffy. He was a nameless pirate that seemed to have a lot of knowledge. Maybe that was the signal it was time for him to help his nephew fulfill what goals he may have. When he heard that Luffy was interested in the One Piece, he probably had to hold back the joy of knowing his sister's will lives on in her son. In the future, I see Black Beard helping Luffy take out Kaido and dealing with any further threat from Big Mom. Shanks appears to fear Black Beard and will not stand in the way of letting Luffy become the King of the Pirates. I would think Shanks know the true relationship as well. Could explain why BlackBeard gave him the scar over his eye. Know who Luffy was meant that Shanks could not let Luffy die, out of respect for Luffy's mother who could have been one of Gold Roger's crew and out of fear of her brother, Marshall D. Teach who would have killed Shanks if Luffy would have died then.