Orbital Drop Shock Trooper

ODSTs are introduced in the fictional world of the Halo video game and book series. Highly skilled and trained, the ODSTs are a special forces outfit (105th Division) of the UNSC Marines.

ODST (Orbital Drop Shock Trooper)
The Orbital Drop Shock Troopers, or "ODST", are an elite special operations unit within the UNSC Marines. Their role on the battlefield is usually described as that of an aggressive shock infantry raid force. As their name implies, ODSTs are dropped from low-orbital positions onto the surface of planets (or in the case of both Halo rings, ancient artifacts), often into combative situations. They are deployed via HEVs (Human Entry Vehicle), one-man pods designed to carry soldiers to their drop point. This unique delivery method makes them collectively less susceptible to enemy ground-to-air defenses than conventional Marines, who have to be ferried to battle in large troop carrier dropships. Once at their destination, the ODSTs have to move quickly in order to regroup, secure a perimeter, and treat the less fortunate of their ranks.

The ODSTs were first introduced and described in the novels based on the Halo: Combat Evolved storyline. However, ODSTs did not make an actual in-game appearance until Halo 2. Although they have sometimes been described as a futuristic science fiction equivalent of WWII Paratroopers, the ODST's primary role is as shock infantry assault in deep enemy teritory. ODSTs are also known as Helljumpers.

The ODSTs wear a special uniform to distinguish them from other Marines. Instead of the standard green, they are clad in gray, with a helmet that includes a face shield (reminiscent of the Sparatans' MJOLNIR Mark VI armor). Their chest armor includes pouches and they have additional leg armor compared to the standard Marine armor in the game. This makes them instantly recognizable as elite troops.

Helljumpers
The 105th Division of the UNSC Marine Corps is an entirely volunteer outfit, and for a good reason. The HEVs, following deployment, heat up immensely due to atmospheric friction, sometimes fatally so. Even if the ODST survives the heat, there's always the chance that his HEV won't. As experienced by Major Antonio Silva in The Flood, the pod's outer layers sometimes get stripped away, leaving the ODST to face the elements with nothing but his combat armor. The third and by far worst forms of a falling ODST's fate is chute failure. The HEV's descent achieves such high velocities that the chance of the parachute failing to slow the pod is an ever-present threat. The HEVs are armored, but not enough so to protect an ODST from an over 400 km/h descent from orbit.
 * Note the name is reminiscent of modern day Smoke Jumpers

Feet First Into Hell
ODSTs (Also known as "Helljumpers") are highly-skilled, versatile, and lightning-fast to deploy, but their job is incredibly demanding and extremely high-risk. Because of the intense(sometimes fatal) heat the Helljumpers have to suffer through with every drop, they adopted the phrase "Feet First Into Hell" as their motto. It symbolizes their willingness to literally jump into extreme danger in order to help others.

ODST Bravado
Also due to the huge risk of their job and the superiority of their training, the ODST's are proud and have a very "gung-ho" attitude.

The ODST's are also known for being extremely brutal, even to fellow soldiers. The reasons may be many, but the general theory is that they believe that other Marines are inferior to them for not signing up for their exclusive elite unit. Many also despise the SPARTAN project, calling the subjects "freaks," because many seem to believe that the bio-mechanically altered/enhanced SPARTANs are not truly human. They do, however, respect the individuals as excellent soldiers. However cruel they are to the other forces, they are the cream of the UNSC crop.

The ODSTs' attitude and bravado were introduced and developed in the novels, but does not appear in Halo 2, in fact the ODSTs don't even have their own dialogue, rather the standard Marine combat dialogue is given to them, and the ODSTs in the game (for their very limited appearance) have no problem fighting alongside the Master Chief.

ODST Origins
The original idea for ODST's comes from the Mobile Infantry in Robert Heinlein's Starship Troopers and from modern day and World War Two Airborne divisions since both serve similliar purposes of disruption of enemy forces to aid the main assult force.