A sailor wants to climb a mast by himself with two ascenders
made of two lengths of rope each tied into a loop.

What is the name of the self-adjusting friction knot for this
purpose that uses two separate loops of line and resembles a
cow hitch?

It is considered to be "the" climbing knot that everything
else is compared to.

What other ascender knots have you used and how did
they work out?