Rambo: New Blood would have been a TV series centered around the adventures of Rambo's son. There have been many unmade Rambo projects over the years, with the original First Blood itself going through various iterations. This includes a period where Steve McQueen was attached to play Rambo. Pretty much every sequel in the series has gone through radically different iterations, such as one version of Rambo 2 set to pair Stallone with John Travolta as a comic relief sidekick.
Rambo 4 also went through vastly different concepts, including the character teaming with his estranged brother to stop a gang of escaped convicts during a hurricane, or a rejected script that was later rewritten as Jason Statham thriller Homefront. Easily the most well-known abandoned idea was for Rambo 5, where Stallone wanted to adapt the horror novel, Hunter. This would have seen Rambo and a team of mercenaries tasked with taking down a genetically engineered monster, but after the concept was ridiculed, the notion was dropped.
For a time between the fourth entry Rambo and 2019's finale Rambo: Last Blood, it appeared Stallone wouldn't return to the series. He stated more than once that he was done with the character, and was happy with where the final scene of Rambo left him. During this gap is when talk of a Rambo: New Blood TV series came up. Fox was set to produce New Blood with Stallone executive producing and playing a supporting role while the story followed his son J.R., an ex-Navy SEAL.
Early reports suggested Rambo: New Blood would focus on the relationship between Rambo and J.R., though Stallone's commitment to the project was seemingly in question. It was also unclear exactly what J.R. would be doing on the show or who he was fighting, and little was heard about it until 2018. First Blood author and Rambo creator David Morrell revealed to Digital Spy that he spent some time developing the series, but it appeared doomed from the start as neither he nor the other creatives could crack the idea.
Morrell had trouble with the basic premise too, stating "Never mind that the whole point is that Rambo had been so traumatized by the war that he couldn't bring himself to have a meaningful relationship, let alone have a child. But we'll just forget about all that." It also appeared J.R. would basically be a version of The Equaliser, which doesn't feel particularly original. Rambo: New Blood didn't move ahead ultimately, while Stallone later returning for Last Blood, which left Rambo's fate open-ended. There was also, infamously, a cartoon spinoff in the 1980s called Rambo: The Force Of Freedom, where the title character and his team stopped a terrorist group every week. Due to being aimed at kids nobody actually died on the series, but despite being a success, The Force Of Freedom was canceled after one season during to complaints from parents over its suitably for younger viewers.