ライダー (raidā) means “biker” | MotiTan Japanese Dictionary

More examples

その店には地元のライダーがよく集まります。so no mise ni wa ji moto no ra i dā ga yo ku atsu ma ri ma su

Local bikers often gather at that shop.

Centers on a person who rides a motorcycle, with the riding activity defining the person.

バイカーbaikā: An informal term for a person who rides a motorcycle.
バイク乗りbaikunori: A casual term for a person who rides a motorcycle.

オートバイに乗る人。ō to ba i ni no ru hito

ライダー (raidā) is borrowed from English rider, a noun formed from ride and the suffix -er for a person who rides.

In English, biker usually means a motorcyclist, while rider can also refer to someone on a horse or bicycle.