Step 1: Core idea.
{Existential therapy} centers on meaning, freedom, authenticity and responsibility in the face of anxiety, isolation and death.
Step 2: Match founders.
The approach was shaped by European {existential analysts} like Medard Boss (and earlier Binswanger) and popularized in the U.S. by Rollo May. Hence “Boss and Rollo” captures its founding lineage.
Step 3: Eliminate distractors.
Carl Rogers founded {client/person-centered therapy}; Fritz Perls founded {Gestalt therapy}. Therefore (A) is correct.
\[
\boxed{\text{(A) Boss and Rollo.}}
\]