Tien enters the story as an enemy and leaves it as one of Earth's most loyal defenders. Tien's profile explains who he is; here we trace his path arc by arc, from the Crane Hermit's budding assassin to the dojo master who agrees to fight in the Tournament of Power.
Dragon Ball
Fortuneteller Baba Saga (episodes 69-83)
The anime introduces him earlier than the manga. In episode 82, closing out the Fortuneteller Baba Saga, he and Chiaotzu pretend to defeat the monster Inoshikacho so a village will pay them, until Goku exposes the scam.
22nd Tournament Saga (episodes 84-101)
In the 22nd Tournament Saga he arrives as the Crane Hermit's student, set on humiliating the Turtle School: he knocks out Yamcha and breaks his leg. On learning that Goku defeated Tao Pai Pai, his master's brother, he is ordered to kill Roshi's students. In episode 94 he faces Jackie Chun, blinds him with the Solar Flare and copies the Kamehameha on sight; the old man steps out of the ring on purpose and talks to him about another path. In the final against Goku, in episode 99, he discovers Chiaotzu is paralyzing his opponent on their master's orders and rebels. He blows the ring apart with the Tri-Beam and, in episode 101, wins the tournament by a hair.
King Piccolo Saga (episodes 102-122)
In the King Piccolo Saga he hunts for the Dragon Balls with Roshi and Chiaotzu, but the demon kills them both. To seal him away he learns the Mafuba, a technique that can cost its user's life; in episode 119 he tries it in the middle of his fight with Drum, fails and is saved by Goku at the last second. In episode 122, badly hurt, he becomes the hostage King Piccolo uses to blackmail Goku.
Piccolo Jr. Saga (episodes 123-153)
At the 23rd tournament, in the Piccolo Jr. Saga, he meets Tao Pai Pai again, rebuilt as a cyborg: in episode 136 the assassin slashes him with a hidden blade, leaving a scar across his chest, and Tien drops him with one punch. In the semi-finals against Goku he splits into four with the Shi Shin no Ken, but in episode 141 his friend finds the technique's weak points and knocks him out of bounds. During the final he blasts a crater with the Tri-Beam so the spectators can take cover.
Dragon Ball Z
Saiyan Saga (episodes 1-35)
In episode 12 Krillin and Bulma convince him to train with Kami. In the Saiyan Saga he beats a Saibaman, then in episode 24 Nappa tears off his left arm and Chiaotzu blows himself up on the Saiyan's back for nothing. To avenge him, in episode 25 Tien fires one last one-handed Tri-Beam and dies without leaving a mark on Nappa.
Frieza Saga (episodes 36-107)
In the Frieza Saga he trains with King Kai: in episode 55 he and Yamcha get through the trials against Bubbles and Gregory. In the anime he also clashes with the Ginyu Force in the afterlife, then comes back to life with the Namekian Dragon Balls, now painfully aware of how far ahead Goku is.
Androids Saga (episodes 118-139)
He spends three years preparing for the Androids and asks Chiaotzu to stay home. In the Androids Saga, though, Android 17 flattens him, Piccolo and Trunks in episode 136.
Cell Saga (episodes 140-194)
His finest hour in Z comes in the Cell Saga. Once Cell absorbs Android 17, Tien pins him to the ground with a barrage of Neo Tri-Beams: in episode 153 Androids 16 and 18 escape, he burns through all his energy and Goku teleports him to safety. At the Cell Games he watches from the side until, in episode 184, a Cell Junior beats him down.
Majin Buu Saga (episodes 200-291)
He skips the 25th tournament, but in the Majin Buu Saga he feels he has to act. In episode 266 he saves Gohan from Buu with the Tri-Beam and protects Dende, then is taken out with a single kick. He dies when Buu destroys the Earth and, once revived, in episode 285 he is among the few friends who answer Goku's first call for the Spirit Bomb. In GT he only makes the briefest of appearances.
Dragon Ball Super
Battle of Gods Saga (episodes 1-18)
At Bulma's party, in the Battle of Gods Saga, he joins Piccolo and Android 18 in attacking Beerus and is beaten like them in episode 7.
Resurrection 'F' Saga (episodes 19-27)
In the Resurrection 'F' Saga he leaves Chiaotzu at home and takes on Frieza's army with Gohan, Piccolo, Krillin and Roshi, as episode 21 shows.
Universe Survival Saga (episodes 77-131)
In the Universe Survival Saga Goku finds him running a dojo full of students. In episode 89 he turns down the Tournament of Power so as not to abandon them, but after the chaos caused by Yurin, a former Crane School classmate, he agrees: the prize money Goku promised, which does not exist, would pay to repair the village. In episode 106, splits into four to track down the sniper Harmira and drags him out of the arena along with himself.
Did you know? After the 22nd tournament Launch falls for his wild side and asks him to live at Kame House, but Tien says no: he will not share a roof with his old master's rival.
Our take
Tien is the character who brings the theme of choice into Dragon Ball. His rebellion in the final, with the title within reach, is the series' first real moral act, and everything else follows from it: the Mafuba attempted knowing it could kill him, the last Tri-Beam against Nappa, the Neo Tri-Beam against Cell.
He is also the Earthling who best accepts his limits. He never becomes the strongest, but each time he picks the moment when his sacrifice counts, and Super rewards him with a teacher's role that suits him perfectly.
Also revisit the profiles of Yamcha, his first victim turned friend, Goku, the rival who changed his life, and Master Roshi, who talked him onto a different path. To follow their stories arc by arc too: Goku saga by saga and Yamcha saga by saga.