Hello, my mother past away.. I thought she put me as the beneficiary.. As I was told since she was still married it goes to the husband but they been separated for over 30 years. So does her 401k goes to him or the beneficiary.

If they were still legally married.. it goes to him. You can not name someone else as a beneficiary though as a secondary beneficiary in case of the death of both parties you could of a 401k retirement plan without their written approval and signature at the time. And its unlikely a spouse would do that. If they were actually divorced.. it would depend upon the terms of the divorce decree.

I do assume that the plan did not predate their marriage. Or that no changes were ever made if it did. I've had 4 since I married and that was specifically spelled out when each of them where started.

"I THOUGHT she put me as the beneficiary". Will? Who is executor?

When you assign someone other than your spouse as beneficiary, the spouse has to agree to it. If there was no assigned benenficiary then it goes to the legal spuse. If there was no legal spouse it would go according to inheritance laws in your state.

Will? Who is executor?

It doesn't matter what the will says - the 401(k) passes to the spouse unless he had specifically agreed in writing to not be the beneficiary. As others have noted - even though they were separated for 30 years, by not finalizing the divorce the husband maintains his spousal rights as beneficiary of his wife's retirement account.