Tekken 5 boasts an impressive roster of 35 characters, and is sadly the last entry of the Tekken series where we get to unlock most of them simply by enjoying the game - not buying dozens of micro-DLCs.

Character Selection Screen, Tekken™ 5
The requirements to unlock all characters in Tekken 5 are simple, you just have to beat the Story or Time Attack mode, using different characters! For example, you will unlock Roger Jr. the 1st time you beat either mode, no matter which character you use. Every time you beat them with a different character, you will unlock another one.
Please refer to each character below, for details on how many times you have to beat Story / Time Attack in order to unlock them.
35 Characters in Tekken™ 5
How to unlock Anna Williams: Beat Story Mode / Time Attack with 2 different characters.
Bio (manual): From childhood, Asuka received training in Kazama Style traditional martial arts from her dear father at his dojo. Along with his other students, Asuka's father taught her how to defend herself and instilled in her strong beliefs in justice and integrity. But when an unknown assailant one day attacked the dojo's students and put her father in hospital, Asuka's life changed for ever. A Hong Kong police detective investigating the incident informed Asuka that the perpetrator was likely to enter the King of Iron Fist Tournament 5, so, in the name of justice, she decided to enter as well.
How to unlock Baek Doo San: Beat Story Mode / Time Attack with 3 different characters.
How to unlock Bruce Irvin: Beat Story Mode / Time Attack with 4 different characters.
Bio (manual): Bryan Fury, a replicant created by Dr. Abel, entrusted himself to Dr. Boskonovitch to receive technological upgrades. Boskonovitch installed a perpetual power generator in the cyborg. Instead of thanks, Bryan killed several people at the facility and then decided to enter the King of Iron Fist Tournament 5, thinking it the perfect test of his newly installed generator.
Bio (manual): When Christie's grandfather was diagnosed with an incurable illness, her world fell apart. Without treatment, the doctors only gave him six months to live. Christie hoped a cure was possible using the advanced technology of the Mishima Zaibatsu, so she decided to enter the King of Iron Fist Tournament 5, seeing it as a chance to save her grandfather.
How to unlock Devil Jin: Beat the Devil Within mode (or play a total of 200 fights while having unlocked all other characters).
How to unlock Eddy Gordo: Purchase Christie's alternate costume through the Customize mode.
Bio (manual): Ambitious without reason, Feng Wei broke the rules of his dojo that forbade him from fighting martial artists or other styles. When his master intervened, Feng Wei mercilessly killed him. Now, seeking to perfect his art of the "God Fist" and recover the secret scroll, Feng Wei enters the King of Iron Fist Tournament 5 and will let nothing stand in his way of victory.
How to unlock Ganryu: Beat Story Mode / Time Attack with 7 different characters.
How to unlock Heihachi Mishima: Beat Story Mode / Time Attack with 9 different characters.
Bio (manual): The Korean army took Hwoarang into custody during the last round of the King of Iron Fist Tournament 4 and forced him to return to the armed services where he served a further two months. When his military service came to an end, Hwoarang was free to pursue a confrontation with Jin Kazama and the King of Iron Fist Tournament 5 would provide the perfect setting.
Bio (manual): A mass-produced fighting machine, JACK-5 uses its robotic brute strength to pummel opponents into a messy pulp. The product of an ingenious physicist, JACK-5 will be more than a match for any competitor at the King of Iron Fist Tournament 5.
Bio (manual): Jin Kazama, the son of fate born to Kazuya Mishima and Jun Kazama, is plagued by recurring nightmares. The bad dreams began after a gruelling battle where Jin left his father and his grandfather Heihachi Mishima behind in Honmaru to await their fate. Since then, the influence of the Devil Gene has grown stronger. Without intervention, it is only a matter of time before Jin will be completely overcome. Perhaps redemption can be achieved through victory at the King of Iron Fist Tournament 5?
Bio (manual): Disappointed that she was unable to recover her research data during the King of Iron Fist Tournament 4, Julia Chang looked for new direction in her forest rejuvenation research back home in America. But it soon became apparent that she desperately needed the lost data. She had a duty to replenish the globe's tree stock and halt deforestation the world over. To fulfill her hopes for forest restoration, Julia decided to enter the King of Iron Fist Tournament 5.
Bio (manual): Having been beaten by both Heihachi Mishima and Jin Kazama in the King of Iron Fist Tournament 4, Kazuya fled Honmaru during an invasion by a battalion of JACKs. Leaving his father at the mercy of the brutal robots, Kazuya took flight just as Honmaru exploded. When the announcement that the King of Iron Fist Tournament 5 was to be held, revenge filled Kazuya's veins and his decision to enter the competition was swift.
Bio (manual): After defeating Craig Marduk, King headed to the boastful Australian's hospital room to finish him off and avenge his master's murder. But at Marduk's bedside, King realised the foolishness of his desire for vengeance and walked away. After Marduk declared his craving for a revenge match at the King of Iron Fist Tournament 5, King roared, "I will not stand by and allow my mentor's name to be disgraced!"
How to unlock Kuma: Beat Story Mode / Time Attack with 6 different characters.
Bio (manual): Bad news followed Marshall Law around like a nasty smell. Having failed miserably in the King of Iron Fist Tournament 4 aand having seen his restaurant business go into bankruptcy, the news that his son has caused a serious accident while joyriding on Paul Phoenix's motorbike came as a new low. To earn enough cash to cover the damage and hospital bills, Marshall Law had no choice but to enter the King of Iron First Tournament 5.
Bio (manual): Lee Chaolan entered the King of Iron Fist Tournament 4 to defeat his adoptive father, Heihachi Mishima. However, it was Kazuya Mishima, supposedly long dead, who defeated a confused Lee. After a failed attempt to take control of the Mishima Zaibatsu, Lee became enraged, "What? Is it Kazuya? He's always in my way!" Motivated by revenge and hatred, Lee entered the King of Iron Fist Tournament 5.
Bio (manual): An Interpol detective from Hong Kong, Lei Wulong was investigating serial rampage incidents at dojos around China when the culprit mysteriously disappeared. After a similar incident in Japan, Lei surmised that the next target would be the King of Iron Fist Tournament 5 and decided to enter the competition himself. Would the detective's deduction be correct, and if so, could he track down the perpetrator before he or she struck again?
Bio (manual): Craig Marduk, undefeated Vale Tudo fighter, was infuriated over his loss to King in the previous King of Iron Fist Tournament. After being released from hospital, he started a harsh training regimen to hone his body into the ultimate weapon. The revenge match will take place at the King of Iron Fist Tournament 5. This time, King will bite the dust!
How to unlock Mokujin: Beat Story Mode / Time Attack with 8 different characters.
Bio (manual): To regain her memory, Nina Williams met with her sister, Anna, for the first time in several years. Upon seeing her sister's face, Nina remember the bitterness of their past encounters and immediately went for her gun. The shootout lasted for days, but neither sibling could make a decisive hit. They decided to settle their fight once and for all at the upcoming King of Iron Fist Tournament 5.
How to unlock Panda: Beat Story Mode / Time Attack with 6 different characters.
Bio (manual): When defeated in the King of Iron Fist Tournament 4, Paul Phoenix realised his problem was overconfidence. He had forgotten some important lessons and strayed from the path to becoming a great fighter. Wanting to rediscover what he had lost, the King of Iron Fist Tournament 5 provided him with the perfect platform on which to prove himself. The engine was still running, it just needed a bit of tuning!
Bio (manual): Codenamed Raven, this international intelligence agent is considered highly skilled and iron-hearted. Apart from a scar in the shape of an "X" on his face, his details, including age and nationality, are unknown. Raven entered the King of Iron Fist Tournament 5 to find out who or what was behind the event, but does he know more than those he reports in to?
How to unlock Roger Jr.: Beat Story Mode / Time Attack once.
Bio (manual): Steve entered the King of Iron Fist Tournament 4 to show off his strength to the world and find out where he came from. With the help of Lei Wulong, he learned the secret of his birth. Having made a comeback as the world champion, Steve immediately decided to enter the King of Iron First Tournament 5.
How to unlock Wang Jinrei: Beat Story Mode / Time Attack with 5 different characters.
Bio (manual): Ling Xiaoyu cried when she learnt of Heihachi's fate. In her sorrow, she wished she could go back in time and alter history. Having met a self-proclaimed genius who boasted he could invent a time machine if only he had the money, Ling Xiaoyu decided to enter the King of Iron Fist Tournament 5 to fund the invention. To go forward, she must first travel back...
Bio (manual): Yoshimitsu, head of the Manji Party, helps the starving people of the world. When members of his party were threatened, Yoshimitsu rushed to their aid, but many members were slaughtered. When Yoshimitsu heard the killer had entered the King of Iron Fist Tournament 5, he sharpened his sword and signed up as well, seeking revenge on behalf of his dead friends.