Fallout 4 Companions

Permanent companions
The game has about a dozen companions, including:
 * Dogmeat
 * Codsworth
 * Preston Garvey
 * Piper

Looking at the E3 reveal trailer, it can be seen that a super mutant is assisting the Sole Survivor in attacking other super mutants on what looks like a high-rise building. It is unknown if this super mutant is a permanent companion, a quest-tied temporary companion, or just a friendly super mutant assisting the Sole Survivor.