A wheelchair or walker apparatus is disclosed and includes a frame having a base portion and spaced side portions to define a space for receiving an operator's body. A device is provided for supporting the frame above a ground surface for movement therealong and includes a mechanism for moving the apparatus over the ground surface. The movement mechanism includes a device for maintaining contact with a ground surface when moving over uneven terrain. The movement mechanism can be maintained in a preferred alignment. A device is provided to permit an operator within the space to control movement of the apparatus along the ground surface. A seat assembly supports and selectively moves an operator between a seated position and a substantially upright position within the apparatus and permits the operator to control and move the apparatus over the ground surface from both the fully seated position as well as the substantially upright position. Additionally, the seat assembly moves horizontally forwardly and rearwardly to aid in ingress to and egress from the apparatus, as well as upwardly and downwardly to adjust to the size of the operator. A back support is provided, which in a preferred embodiment, tilts as the operator moves from a seated to a substantially upright position.