Complex sentence: His surname is derived from the forename of Krum, a successful khan that ruled Bulgaria in the 9th century, although it being a surname suggest the-ov family suffix, and its absence makes the name look odd or unnatural to a Bulgarian.
Split into simpler sentences: His surname is derived from the forename of Krum, a successful khan that ruled Bulgaria in the 9th century; unlike most Bulgarian surnames, it lacks the suffix "-ov". This absence makes the name look odd or unnatural to a Bulgarian.