Orca

The Orca is a giant killer whale that pursues Sonic in certain Sonic games. It is the first of many objects that Sonic must outrun in 3D and 2D Sonic games.

Sonic Adventure
The Orca first appears in Sonic Adventure in Emerald Coast. It chases Sonic across the wooden planks on the water in the famous "Orca Chase".

Sonic Heroes
Two orcas appear in Seaside Hill and jump over the road just beyond the third island. They are smaller than the first one and don't seem to have a grudge against Sonic.

Sonic 06
The Orca appears in Wave Ocean and again chases Sonic across wooden platforms. Sonic hangs onto its dorsal fin and flings off when Tails closes the gate to keep the Orca inside.

Sonic Generations
The orca returns in Sonic Generations in both Emerald Coast and Seaside Hill.

In Emerald Coast, the Orca is once again chasing Sonic (Classic in 2D and Modern in 3D) to eat him up. With Classic Sonic, it chases him through a broken bridge as Sonic runs and jumps through it to avoid getting eaten or falling in the water.

With Modern Sonic, the orca is more agressive, as at the end of the level, the orca jumps out of the water in a last attempt to eat Sonic. Sonic then performs Combo Tricks to avoid the orca's bites and finally reaches a platform, which the orca hits with it's head and falls back into the water.

In Seaside Hill, the 2 orcas are back to help the Sonics. With Classic Sonic, they help him to get across the water after he is launched from a cannon. With Modern Sonic, they sometimes jump out of the water when they see him running through and help him reach the end of the level after he gets launched off a ramp.