|Relationship||Kuki Sanban (obvious childhood crush, married as adults)|
|Family||Mr. Beatles, Mrs. Beatles, Joey Beatles (baby brother), Toiletnator (long-lost uncle)|
|Friends||The rest of Sector V|
|Enemies||Villains, Ernest, King Sandy, Toiletnator, The Kid (whenever he flirts with Numbuh 3)|
|Nicknames||"Wally", "Sport" (called so by his father)|
|Voiced by||Dee Bradley Baker|
Wallabee "Wally" Beetles a.k.a. Numbuh 4 is the brash and impulsive hand-to-hand combatant Australian boy of Kids Next Door Sector V. He is close friends with Numbuh 2 and has a crush on his teammate, Numbuh 3.
Wally is easily recognizable by his blonde hair with its bowl-shaped cut. He wears an orange hooded sweater and blue jeans. His eyes, like almost the entire Sector V, are not always visible. He is also the shortest Sector V member, for which he is picked on a lot (for example, Numbuh 5 called him "sport" in Operation: M.A.T.A.D.O.R.). Another identifiable trait is his Australian accent.
Numbuh 4 is the team's bravest, toughest, strongest, fiercest, wildest, most adventurous, dangerous, courageous, and possibly the best fighter in Sector V. He is also the most impulsive, brash, hot-headed, arrogant, ignorant, and harshest of the team. As a result, it is stated in Operation: F.U.T.U.R.E. that his parents would send him to military schools, but he would always bust out.
As seen in Operation: C.A.N.N.O.N. and Operation: F.E.R.A.L., Numbuh 4 has the desire to become leader of Sector V, but fails due to his bossy attitude. Nevertheless, Numbuh 4 values his friendship with his friends and cares deeply for them as seen in Operation: P.O.O.L. and even shed tears in Operation: M.A.U.R.I.C.E., when Numbuh 9 was being decommissioned.
Despite not being the most book smart, he is indeed the operative with the most street smarts, along with Numbuh 5 as shown in Operation: M.A.U.R.I.C.E.. Numbuh 4's passion is sports as shown in Operation: F.O.U.N.T.A.I.N., Operation: M.A.T.A.D.O.R., Operation: D.O.D.G.E.B.A.L.L., and in Operation: B.R.E.A.K.U.P., which is basically the only thing he is good at besides fighting. As it is mention throughout the show, Numbuh 4 has a terrible fear of swimming, but was barely able to learn in Operation: P.O.O.L.. As shown in Operation: S.A.F.E.T.Y., Numbuh 4 is hemophobic, having an extreme fear of blood and faints at the sight of it.
As the team's hand-to-hand combat specialist, he the most capable when it comes to physical fighting, but is the least intelligent KND operative as shown in several episodes, including Operation: E.N.D., Operation: D.O.G.H.O.U.S.E., Operation: S.P.R.O.U.T., and Operation: Z.E.R.O., which leads to him being easily fooled, and usually selected for dangerous parts in missions. In Operation: S.P.R.O.U.T., when Numbuh 1, Numbuh 2, and Numbuh 5 were inside of him, it was shown that he had a very small brain. Despite this, Numbuh 4 has a strong sense of determination and never gives up in a fight.
However, there are some moments where he shows some intelligence. In Operation: P.O.O.L. when the evil versions of the KND (known as the DNK, Destructively Nefarious Kids) posed as his friends, he was able to tell that they were impostors when he looked into Negative Numbuh 3's eyes. He was also able to realize the evil version of him, Negative Numbuh 4, was a coward after discovering that the evil versions of the KND were the opposites of the normal ones.
Numbuh 4 has a strong dislike for everything girly, including Rainbow Monkeys, especially since Rainbow Monkeys make Numbuh 3 giddy. However, Wally begrudgingly tolerates her obsession to keep her pleased, due to his obvious crush on her.
He also is shown to be very jealous when someone tries to flirt with Numbuh 3, as seen in Operation: L.O.V.E. and Operation: C.A.K.E.D.-F.O.U.R.. There were many times in the show when Numbuh 4 came close to confessing his love to Numbuh 3, such as in Operation: L.O.V.E., Operation: H.O.S.P.I.T.A.L., and Operation: B.E.A.C.H. , but is never able to finish, due to interruptions or an unwillingness to go on.
- Father: Sid Beetles
- Mother: Mrs. Beetles
- Siblings: Joey Beetles
- Future Wife: Kuki Sanban
- Uncle: Lou/Toiletnator
Numbuh 2 and Numbuh 4 have been good friends, starring together in many episodes near the end of the series (such as Operation: S.A.F.E.T.Y. , Operation: B.U.L.L.I.E.S. and Operation: F.I.S.H.Y.). Numbuh 2 is also aware of Numbuh 4's crush on Kuki (aka Numbuh 3) and would often tease him about it with Numbuh 5 throughout the show.
It has been hinted throughout the series that Numbuh 4 has a crush on Numbuh 3, and vice versa. They are polar opposites, with Numbuh 3 being a girly-girl and obsessed with Rainbow Monkeys all things feminine, and Numbuh 4 being into what, stereotypically, younger boys like, such as violence and germs. He's shown many hints of attraction as he has blushed whenever she hugs him or even says a comment that flatters or embarrasses him. In Operation: I.N.T.E.R.V.I.E.W.S., this relationship with her becomes canon as it reveals that he married Numbuh 3.
- Numbuh 1 Disguise (Operation: C.A.N.N.O.N., Operation: Q.U.I.E.T. )
- Sheriff Gear (Operation: N.U.G.G.E.T.)
- Spank Happy Vampire (Operation: L.O.C.K.D.O.W.N., Operation: V.I.D.E.O.G.A.M.E. )
- Numbuh Four Thirtyteen Seven (Operation: S.L.U.M.B.E.R.)
- Matador Costume (Operation: M.A.T.A.D.O.R.)
- Mr. Huggikins (Operation: C.A.T.S.)
- Numbuh 4's last name, Beetles, is a reference to his codename, as the band The Beatles had four members (even though The Beatles originated from the UK, and Numbuh 4 is Australian).
- Numbuh 4's hairstyle is also very similar to the styles of the Beatles in their early years.
- Numbuh 4 is allergic to coconuts, as seen in Operation: O.U.T.B.R.E.A.K., causing him to react with swollen lips.
- He was seen old with grey hair in Operation: F.U.T.U.R.E., Operation: W.H.I.T.E.H.O.U.S.E. (though his age was the same as Numbuh 1,2,3 and 5) and Operation: Z.E.R.O. as a Senior Citizombie. So far, Numbuh 4 has the most future selves seen in the series and movie specials, with a total of six.
- His most prized characteristic, according to Operation: C.A.R.A.M.E.L., is his ferocity, which is a bit simplistic, but very strong.
- A drawing of Kuki is seen in his room near his window in Operation: M.O.O.N., then a picture of a green number 3 with hearts can be seen in the background of his room near a hockey stick, most likely referencing his crush on Numbuh 3 as well. These drawings have been seen in a few more episodes than mentioned.
- He and his brother are named after marsupials found in Australia.