BBCIf you ask most contemporary Doctor Who fans who their favorite Doctor is, the answers will be mixed. But, if you ask any fan to objectively say which modern Doctor was the most pivotal for turning the series into a mainstream worldwide phenomenon, the answer would have to be David Tennant. While it's arguable that Matt Smith’s era from 2010 to 2013 represented the peak of Who’s viewership, it was David Tennant’s three-season run from 2006 to 2010 that energized and largely created that fanbase. And like the non-linear nature of the Doctor’s various adventures, it’s sometimes hard to pinpoint when the 10th Doctor actually began. Yes, he appeared at the end of the Season 1 finale “The Parting of the Ways” in 2005, and then had his first proper appearance as the Doctor in the 2005 special “The Christmas Invasion.” But, the first real-deal 10th Doctor adventure, complete with the skinny suit, the coat, and all the catchphrases, was Tennant’s third outing in the role, the Season 2 debut “New Earth.”On April 15, 2006, “New Earth” began, in earnest, what was to become one of the most iconic runs of Doctor Who ever, and set a standard by which much of the subsequent seasons were measured. But, does “New Earth” really hold up? And, by extension, does this classic season of Doctor Who really contain the best of what the series has to offer?“New Earth” relaunched Doctor Who in 2006. Again. | BBCFollowing the Doctor’s regeneration episode in 2005’s “The Christmas Invasion,” the events of “New Earth” pick up in the next moments with the Doctor taking Rose (Billie Piper) on their first new adventure together. It’s strange to think of this, but at the time, it was arguably Piper in this moment, not Tennant, who was the bigger star; in addition to having already starred in Season 1 of Doctor Who alongside Christopher Eccleston, Piper was already a successful pop star. Tennant, meanwhile, was probably most famous to international (read: not U.K.) fans for his brief role as the villainous Barty Crouch Jr. in Harry Potter and the Goblet of Fire in 2005. Today, Tennant is geek royalty, but 20 years ago, “New Earth” was his proving ground.No sane fan would ever call “New Earth” one of the best episodes of Doctor Who, and in a way, it's a redo and a sequel to the far better Season 1 (2005) episode “The End of the World.” Instead of going to the last days of Earth, the Doctor and Rose journey to a new version of Earth, complete with a New New York, which is the 15th version of the city. Humanity is very nostalgic about recreating entire cities and planets in the future, which gives the episode very strong Douglas Adams vibes. Tennant also spent most of “The Christmas Invasion” in his bathrobe, which is also very Arthur Dent in Hitchhiker’s Guide, and of course, Adams himself wrote for Who in the 1970s.David Tennant, Russell T Davies, and Billie Piper in 2006. | BAFTA/Getty Images Entertainment/Getty ImagesThe point is, there’s a zany sort of intentionally unrealistic silliness to “New Earth,” so much so, you might think that Doctor Who was becoming a sitcom first and a sci-fi adventure show second. The Doctor and Rose once again encounter Cassandra, the last human, who is just a sheet of skin with eyes and a mouth. Eventually, this turns into a body-swapping episode, in which Cassandra inhabits the body of both the Doctor and Rose, at various points, in which hilarity should result. (One working title of the episode was even just “Body Swap.”)The thing is, 20 years later, Tennant pretending he’s been taken over by the consciousness of Cassandra is not his finest hour, and, if you’ve already seen his entire run, you’ll know that Tennant’s comedic chemistry with Catherine Tate as Donna Noble is way better than any of the gags here with Rose. On its face, “New Earth” is an episode about a space hospital, body-swapping antics, and, in theory, a fairly glib message about how people shouldn’t get too much plastic surgery. You can, in theory, watch a better David Tennant Who episode than this by accident.But we can’t call “New Earth” a bad episode, and that’s because it establishes so much about the tone and direction of what would become the gold standard for modern Doctor Who. This episode finds Tennant on a joyful, moralizing high horse, in which he is both a clown and somehow an unforgiving judge capable of the ultimate sanction. While Eccleston’s biting 9th Doctor wit felt like less of a contrast with his occasional cruelty, Tennant gives the 10th Doctor mood swings that are more pronounced; he’s both a nicer version of the Doctor and one who is much more arrogant. Then-showrunner Russell T Davies seemed to want to transform the Doctor into a new type of dangerous alien hero: With the 9th Doctor, the character was a bitter battle veteran with a heart of gold. But the 10th Doctor was a puckish “lonely God,” which, in retrospect of knowing his entire arc, makes him slightly scarier. “New Earth” also does a decent amount of heavy-lifting for the lore-building for the rest of the show; the mysterious “Face of Boe” reappears here, after being introduced in “The End of the World,” the previous season. By Season 3, when the Doctor returns to New Earth, Boe would return, again, tying together a variety of plot twists and turns that either do or don’t work, depending on your opinion of the ending of Season 3.The point is, the best and worst of the Tennant era are all contained and previewed here in “New Earth.” If there weren’t several other better options available from the run of the newer seasons, you could even argue that “New Earth” is a good way to introduce someone to the vibe of Doctor Who, again, not because it’s a great episode, but because it does have a tone and style that pervades much of the rest of Season 2, and the Tennant era more broadly.The Doctor probably puts it best early in the episode, calling himself the “New New Doctor.” This was a metafictional nod: Who had only rebooted the year prior in 2005 with Christopher Eccleston, and now, with a real second season underway, audiences were asked to accept another new Doctor, already. By the end of 2006, Tennant would become the most popular actor to play the character since Tom Baker. And even though “New Earth” is no banger, his performance in this episode proves why, to this day, we still can’t get over him. He’s goofy. He’s scary. He looks great in the skinny suit. This was the true reinvention of the Doctor, and, at the end of the day, it didn’t really matter if the story was memorable. Tennant’s Doctor was all about the vibes, and in April 2006, those vibes were pushing the TARDIS into a brave new era of global popularity.Doctor Who (2006) is currently available to rent or buy on Apple TV, Prime Video, and elsewhere.