Many players are tasked with protecting the quarterback, but the main positions are on the offensive line. The offensive line is made of five positions, and depending on the defensive scheme, sometimes six. The positions on the offensive line are the left tackle (LT), left guard (LG), center (C), right guard (RG), and right tackle (RT). These are the principal players that will have the job of protecting the quarterback no matter what. Those positions also have to protect the running back if a running play is called.
Sometimes the tight end (TE) may line up on the offensive line and help the offensive line in protecting the quarterback on a pass play or protect the running back on a run play. Tight ends can leave the offensive line and be an eligible receiver to catch a pass, but offensive linemen cannot.
The running back can also protect the quarterback if necessary, and will usually do so when linemen fail on certain blocks. The running back can also leave the backfield and catch a pass, just like the tight ends.
The offensive line as a unit is tasked with protecting the quarterback. However, the quarterback has what's called a 'blind side', which is the side of the offensive line towards their back. For example, if a right-handed quarterback's blind side is the left side of the offensive line, he will have his left foot in front of his right foot when throwing the ball. For left-handed quarterbacks, the right side of the defense is the blind side. The position meant to protect the blind side is the tackle position.