Industrial chemist Lieutenant Colonel Andrew Blodgett "Monk" Mayfair and his pet pig, Habeas Corpus. Monk got his name from his simian appearance, notably his long arms, and he was covered with coarse, red hair.
Lawyer Brigadier General Theodore Marley "Ham" Brooks and his pet monkey, Chemistry. Ham (the shyster, as Monk usually referred to him) got his name after teaching Monk some French swear words to innocently use on a French general. Shortly afterwards, a large joint of ham went missing and turned up among Brooks' things, so he was blamed and got that nickname.
Construction engineer Colonel John "Renny" Renwick. Renny had fists like buckets of gristle and bone and no wooden door could withstand them.
Electrical engineer Major Thomas J. "Long Tom" Roberts. "Long Tom" got his nickname from an incident with a World War I cannon of that nick-name. Long Tom was a sickly-looking character, but fought like a wildcat.
Archaeologist and geologist William Harper "Johnny" Littlejohn. Johnny used long words ("I'll be superamalgamated!" was a favourite saying). Johnny wore a monocle in early adventures (one eye having been blinded in World War I). Doc later performed corrective surgery.
[The Fabulous Five in James Bama's famous Bantam Books back cover illustration above; left-to-right: Ham, Johnny, Renny, Long Tom & Monk.]