Parents, that is.
There have been many situations during my adult life where I've needed my mom and dad and they've willingly dropped everything to rush to my aide (just this past week for one). And I am so very thankful for them - although I'm sure my expressions of gratitude are quite inadequate. But that doesn't seem to matter to them. Because I know the next time something comes up - preferably something a little less stressful and a lot more fun - they will be right there ready to lend a helping hand.