Where I grew up in the middle of nowhere, the Irwin Allen show was pretty popular mostly because -- if I remember correctly -- it was one of the first live-action shows on television right after school. (No, no, and no: this isn't first-run, but rather this was the days when the program was syndicated.) So if you wanted to watch something in between school time and supper time then the hour-long Lost In Space fit the bill pretty perfectly. While I was never that big a fan of it, I'll admit to watching quite a bit of the episodes over and over and over again, and that was because it fit the bill for reasonably interesting Science Fiction of that bygone era.
Mark Goddard was Major Don West, a kinda/sorta younger version of what William Shatner was doing with his 'captain' over on that other, more cerebral franchise; and it's pretty clear that his character was always intended to be that young, brash hero who'd rush in to save the day against all odds and maybe even his own personal safety. Sadly, that kind of (cough cough) "toxic masculinity" would seem to be in short supply these days, but for those of us who grew up at a time when men were men Goddard played his part perfectly ... and he stole the heart of a young Robinson lady along the way.
Alas, none of us lasts forever, and I just noticed this morning that the actor has sadly passed away.
He continued working well after his time aboard Lost's three seasons in the Final Frontier, but I suspect that those of us who grew up in that generation will always remember him out there doing what he could to keep himself and the Robinson family safe from some of television's weirdest creatures. Hopefully those memories will always bring a smile to the face of fans everywhere.
Our deepest sympathies are extended to the family, friends, and fans of Mr. Goddard.
May he forever rest in peace.