An ode to Radia Perlman
Radia Perlman invented the Spanning Tree Protocol in 1985. She made it possible for networks to have redundant paths without loops. Before STP, adding a second cable could bring down the entire network.
I think that I shall never see
a graph more lovely than a tree.
A tree whose crucial property
is loop-free connectivity.
Radia Perlman, "Algorhyme" (1985)