blackguard = blaggard = blagger

The word is blackguard (pronounced blaggard) and means rogue, villain, or dodgy character.
The term seems to date from the 1500s but became used more frequently in literature in the 1800s.

Sometimes spelled as it sounds blaggard
or just blagger, both of which are non-standard spellings.

Most likely originating in the "brigade" of scullions, kitchen knaves and shoe shine boys who roved
the streets making a little money on the side in unscrupulous ways. The term blackguard was eventually applied to the criminal class.