Marmota monax - from the marmot family. Fat, funny and apparently, quite fierce when provoked.
Things I did not know about groundhogs:
Despite their heavy-bodied appearance, groundhogs are accomplished swimmers and climbers, and climb trees to escape predators or survey their surroundings. They prefer to retreat to their burrows when threatened; if the burrow is invaded, the groundhog tenaciously defends itself with its two large incisors and front claws.
Groundhogs are generally agonistic and territorial among their own species, and may skirmish to establish dominance. Outside their burrow, individuals are alert when not actively feeding. It is common to see one or more nearly-motionless individuals standing erect on their hind feet watching for danger. When alarmed, they use a high-pitched whistle to warn the rest of the colony, hence the name "whistle-pig." Groundhogs may squeal when fighting, seriously injured, or caught by an enemy. Other sounds groundhogs may make are low barks and a sound produced by grinding their teeth.
Me? I just squeal with delight when I see them. They'll be hibernating soon, so seeing them now will be a rare sight.
Update: OK - I admit it. I just had to see if there was a You Tube of these little critters and to my amazement, there was - of baby groundhogs!!