Marvel Studios reveals they have different names for the versions of Thanos featured in Avengers: Infinity War and Avengers: Endgame. When audiences first saw The Mad Titan in the mid-credits scene for The Avengers in 2012, the purple giant was teased as a threat unlike anything the Avengers have or would face. After a few more small appearances in Phase 2, Thanos arrived and lived up to that promise in 2018's Avengers: Infinity War.
After several years of fans asking why Thanos hasn't been more proactive in getting the Infinity Stones, he arrived with a plan to achieve his ultimate victory. He conquered multiple worlds, gathered all six Infinity Stones, and wiped out half of all life across the universe. Satisfied with his work, he destroyed the Stones and didn't fight back in his weakened state when the Avengers arrived. While he died there in 2018, the time travel story of Avengers: Endgame allowed for a different version of Thanos to return. This slightly younger take was in the midst of conquest and learned that he would one day achieve his goals.
Through this storytelling mechanic, Avengers: Infinity War and Endgame presented audiences with two different portrayals of Thanos. For their part, Marvel Studios has a clear divide in these two versions of the Mad Titan. In the newly released The Art of Avengers: Endgame book, concept artist Wesley Burt revealed the difference, "He was always referred to as Warrior Thanos, as opposed to the Philosopher Thanos that would be in Infinity War."
Although Thanos never is addressed by these names in the movies, they do illustrate the different mindsets he had in each film. The Thanos that arrives to achieve his goals in Avengers: Infinity War knows exactly what he wants to do and doesn't waste a moment. Once he accomplishes his tasks, he immediately moves on to the next one instead of prolonging ongoing fights. This works as a stark contrast to the Thanos from 2014 in Avengers: Endgame. He approaches the threat of the Avengers straight out of a major battle and has that warrior mindset throughout the film. This Thanos has seen a future where he's won and believes his actions to be inevitable and acts accordingly.
These differences and the way Marvel Studios perceives the two versions of Thanos is an important aspect of the character to remember moving forward. Even though Philosopher Thanos is very much dead, there are opportunities for both versions of Thanos to return. Movies like Eternals set in the MCU's past could show a much younger version of Warrior Thanos, while a Nova movie showing Richard Rider fight as Xandar is destroyed could also see Philosopher Thanos acquire his first Infinity Stone. Meanwhile, theories that Warrior Thanos isn't actually dead may be more likely to come true. All we don't know right now is when Warrior Thanos makes the transition to Philosopher Thanos, but perhaps we'll learn that in future MCU stories.