The short story:

A Wolf Shapeshifting Military Robot.
Builded from Silent's "Memory" using the "Zeewolf Badge" received from
Roseate Flourish Lefty Sonic's Shop.
The Robot is programmed to protect Silent "The Player/Avatar" at all cost!
He's on the "Night Resistance" side.

His Forms in Fiercy Forces:

1st Shape: Militarycopter Zeewolf ("Buddy" Form)

2nd Shape: Liquid Metal Wolf ("Animal" Form)

3rd Shape: Zeo Metal Zee ("Robot" Final Form)

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Especially... his Duty is to protect Silent "The Player/Avatar" before:
Leo Metal Sonic ("Evil Empire" side and Rival)

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Fun Fact:
The Form "Militarycopter Zeewolf" is based on the series of
Zeewolf & Zeewolf 2: Wild Justice (Amiga Platform).
As well, the Form "Liquid Metal Wolf" appearance is as a reference of
Transformers: Beast Wars series.