Major Matt Mason (and buddies) were astronauts and explorers. They were wire-framed / rubber action figures and were known for their wires breaking and not being able to pose any more!
There were lots of extra gadgets available if you had lots of cash (or rich parents) and I think they were a spin-off from a series of books. Major Matt Mason had a white space suit and the others' were orange and possibly blue (lower ranks I think!).
I remember lusting after the moon vehicle but it was expensive so I lusted in vain and made do with smaller accessories. My brother and I were the only kids on the estate to have this toy since everyone else had Action Man.
Major Matt Mason was produced by Mattel and came out around the same time as the first manned lunar mission as Major Matt Mason was an astronaut who lived and worked on the moon. Other figures in the Major Matt Mason line included Sgt. Storm (blonde hair with a red suit), Doug Davis (yellow suit and brown hair), Lt. Jeff Long (African-American with a blue suit). There was also an alien figure called Captain Lazer along with a "Moon Base".