This is a summery of Tikal's role in the Sonic Games.
Sonic Adventure/Sonic Adventure DX
About 4,000 years ago, Tikal the Echidna was the daughter of Chief Pachacamac of the ancient echidna tribe. Since Tikal's mother died, she was raised by her grandmother, who passed on everything she knew to her. Since Tikal respected her grandmother and believed everything she taught, Tikal also became a pacifist.
Since her father was greedy and power-hungry, she begged him many times to stop his ways, saying that it wasn't the right path to peace. Unfortunately, her father never listened, so Tikal sought peace from her frustration at the Master Emerald shrine near the Mystic Ruins (Angel Island had not floated into the sky yet). She would play with the Chao that lived there and talk to the water spirit, Chaos.
Later, Pachacamac realized that the Chaos Emeralds and the Master Emerald at the shrine could give his tribe total power. One night, Pacahamac and a group of his warriors went to the shrine, which was on fire. Tikal pleaded with them to stop, saying that once they had greed, they would always want more. Pachacamac didn't listen and ordered his men to charge forward. The warriors knocked down Tikal and killed many Chao on the way.
However, as they approached the Master Emerald, Chaos emerged from the ground as a puddle, and since he was the Chao's guardian, used the Chaos Emeralds to turn into Perfect Chaos to kill the warriors to avenge the Chao.
Later, Tikal woke up and noticed that Chaos was wreaking havoc on the world. She immediately ran to the Master Emerald, and remembering a wise saying from her grandmother, requested that the Master Emerald stop Chaos. The Master Emerald then trapped Tikal and Chaos's soul in it. In the Master Emerald, no time passed for them, so Chaos's anger was not cooled. The remaining echidnas that lived made it their duty to protect the Master Emerald so Chaos wouldn't be released again.
Many, many years later, however, the echidnas began to die out. Finally, the only one left alive was Knuckles.
A few thousand years later, Dr. Eggman found the ancient tablets describing the event and went to shatter the Master Emerald to free Chaos so he could obtain world domination. When the Master Emerald broke, Tikal (in the shape of a glowing ball of light) was free. She then subsequently sent Sonic and friends to her past to show them the events that took place in her past.
When Chaos acquired all seven Chaos Emeralds, he became Perfect Chaos and attempted to destroy Station Square because he was still angry.
Tikal then showed her true form and told Sonic that Chaos must be sealed inside the Master Emerald again or else he will destroy the world again. Sonic, however, said that Chaos would still be in turmoil and instead used the positive energy of the Chaos Emeralds to become Super Sonic to defeat Chaos.
When Chaos was defeated, he turned back to normal and Tikal explained that the Chao now lived in peace with everyone. Then Chaos and Tikal rose into the air and disappeared.
Tikal has not been seen since in the storyline, and it is not known where she and Chaos went, but the image after the Super Sonic story credits might suggest that she went to Angel Island.
Sonic Adventure DX Chao Minigame for GBA
The object of this game is to help Cheese find a certain Chao. However, they all look the same. Here, Tikal appears on the field as a pink ball of light, but she regains her true form when you talk to her. She gives you clues as to which Chao you're looking for by explaining to you what they are doing.
Sonic Adventure 2/Sonic Adventure 2: Battle
Here, Tikal and Chaos are playable in 2P mode. In the Dreamcast version, Tikal must be unlocked by getting all of Knuckles' A ranks, but in the Gamecube version she is already playable.
Sonic Pinball Party
In this game, Tikal appears as an animated figure carved in stone in one of the levels.