Guards are NPCs. There have been several different types of Guards who've shown up over the course of the Darths&Droids campaigns and were identified solely as "Guard" in the Da&Dr transcripts.
Silence of the Clones Edit
The first such Guard was a guard for Senator Padme Amidala. He was on the ship Padme, Jar Jar Binks, and R2-D2 were on as they were heading to Coruscant to vote on creating a Grand Army of the Republic.
After the ship landed, the Guard warned Padme that there were rumors of an attempt on her life. Padme ordered R2 to search for traps. R2 replied in the affirmative. Padme's current loyal decoy, Corde confidently walked down the boarding ramp, when suddenly it exploded, right under her. R2 claimed that he thought Padme told him to look for Schnappes. Since the Guard was standing right behind Corde when the bomb went off, he was caught up in the explosion. Since Corde died in the explosion, it's most likely the Guard was killed too.
Revelation of the Sith Edit
There were Guards attending Chancellor Palpatine when he went to see a charity concert for the refugees of the Trade Federation's second invasion of Naboo. When Anakin showed up to talk to Palpatine, Anakin told the Guards to leave. One of the Guards asked Palpatine, "Sir?" Palpatine told him to do as Anakin said, and the Guards left.
When Yoda went to confront Palaptine over the massacre of the Jedi, Palpatine's guards tried to confront him. Yoda simply used the Force to push them into a wall, knocking them out.