tucking them in over and over

a serious question about biters

My three year old has me at my wit's end tonight. He bit three different people today.

One sibling.
One high-schooler.
One little guy- not a brother.

It is not very fun to be the mom that says, "So you might see some teeth marks on your little guy's arm today.  Yeah, sorry about that. My guy bit your little guy for no reason."

I could really use your advice, friends. If any of you have had "biters" before, please share your wisdom with me.

Cute smile. Strong jaws.
A few things about this child:
- he's generally quite happy and sweet
- he has a temper that flares HOT and quick- this sometimes leads to angry biting
- he loves to wrestle and play on the trampoline- this sometimes leads to excited biting
- he has bitten completely unprovoked- including the baby minding his own business! bored biting?!
- he also pinches (hard) in these situations, too.

- other words to describe this kid: Happy, cuddly, cheerful, compliant, affectionate, eager-to-please (and this is why this confuses me so much!)

Tips? My mind and ears are open!