X-5 (voiced by Canadian actor Bruce Hunter), is the third member, and robot of Atomic Betty's crew, and is a roughly rectangular headed, bright yellow colored, hovering robot, who takes the role of both the navigator for the Starcruiser and providing any unknown information that they may need for their mission. Due to being a robot, he tends to sometimes spout too much information at inopportune times and takes most things (especially his missions) exceptionally seriously, which usually gets on his fellow crew member Sparky's nerves, and sometimes even Betty's as well. The two of them have a grudgingly respectful working relationship.
Though it is often implied in the TV series that X-5 is an outdated model of Galactic Guardian robot, newer, more advanced model Galactic Guardian robots that have been debuted in episodes, such as X-8.5. in the episode Bye-Bye X-5, have tended to be less reliable. In the third season, he also becomes a scientist and inventor, working in the lab in Galactic Guardian Headquarters with the Bangoons (and also Noah in the third season's Crash Test Noah! shorts) as his test subjects and his assistants, and inventing new gadgets that are used by Betty on her missions. He also dons a disguise sometimes to make him look somewhat like a human. When he visits Betty's home, he tries to "improve" upon the appliances in Betty's house while cat-sitting, as in the Season 3 episode Aarrgh...It Be 'Olidays!, thinking that the house's technology (like most technology on Earth) as being primitive.
- Admiral DeGill - commanding officer
- Sparky - boyfriend, also alien crewmate
- Betty Barrett - human friend
- Noah Parker - human friend
- Maximus I.Q. - rival
- Minimus P.U. - rival
- B-1 - uncle
- B-2 - father
- Before meeting his "Uncle" B-1 during the events of the first season episode "Battle of the Bots", and the events of the first season, X-5 thought he was a orphan.
- X-5 made an appearance in PowerPuff Girls Doujinshi. X-5 did not make it out of the "abandon" ship in one piece as Protoboy slashed his head right off and started to rip his body apart. Betty was able to get his head.
- In the show's revival onward, it is revealed that X-5 will live with his "Uncle" B-1 and "Father" B-2.