Orcas (also known as Killer Whales) are large aquatic mammals that pursue Sonic in certain Sonic the Hedgehog games. It is the first of many objects that Sonic must outrun in 3D and 2D Sonic games.
The orca first appears within Emerald Coast in Sonic Adventure. It chases Sonic across the wooden planks on the water in the famous "Orca Chase".
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.
The orca appears in Wave Ocean and again chases Sonic across wooden platforms. Sonic hangs onto its dorsal fin and gets flung off when Tails closes the gate to keep the orca inside.
The orcas 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 aggressive, as at the end of the level, it 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, where the orca bangs its head and falls back into the water.
In Seaside Hill, the two orcas return to help the Sonics. With Classic Sonic, they help him 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.
Sonic & All-Stars Racing Transformed
Ocras return in the sequel to Sonic & SEGA All-Stars Racing in the stage Ocean View. They don't harm the player nor do they affect the track, but they do flips above the track to get to the ocean.
This is a cold-blooded killer, and resembles an actual killer whale, being one of the few(if only) non-anthropomorphic Sonic characters in-game. It has basic predatory instincts, and is determined to capture Sonic, relentlessly pursuing him.