ODST

The ODST is a class of soldier seen in the Halo franchise.

Halo 2
This is the first game appearance of ODSTs. Sometimes, they appear as a replacement for regular troopers. In Delta Halo, these soldiers drop in with pods along with the Master Chief.

Halo 3
ODSTs appear in this game, though they are never seen dropping in pods.

Halo Wars
The ODST appears in Halo Wars, as Captain Cutter's main infantry. In gameplay, the wield shotguns. The player can have them drop into battle.

Halo 3: ODST
ODSTs are more prominent in this game. Six identified troopers appear in the game as playable characters.

Lance Corporal "The Rookie" (real name unknown)

Gunnery Sergeant Edward Buck

Taylor "Dutch" Miles

Kojo "Romeo" Agu

Michael "Mickey" Crespo

Veronica Dare

Halo: Reach
ODST Bullfrogs appear in this game, as a special unit. They have jetpacks.

Trivia
A dead ODST can be seen in the level Cortana. It's as though he trekked through the Flood-Infested High Charity. A flamethrower is seen near this corpse.

The ODST armor permutation as available in Halo IV's Infinity Armor Pack.

The Rookie dies.

The ODST helmet is available in Halo 3.

ODST helmet shoulder pieces and chestplate are available in Reach.

In Halo Wars gameplay, a full squad of ODSTs drop from one pod. (It's as though they use Covenant Squad Pods.)

Some cosplayers dress up in ODST costumes.