The question asks which philosopher emphasized the primacy of ethics. To determine the correct answer, let's explore each philosopher's contributions and focus:

• Edmund Husserl: Husserl was the founder of phenomenology, a philosophical approach that emphasizes the direct examination and description of phenomena as they are experienced. His work primarily focused on the structures of consciousness and epistemological questions rather than ethics.
• Martin Heidegger: Heidegger is known for his work in existential philosophy, particularly his book "Being and Time." His philosophical focus was on ontology (the study of being), though he indirectly addressed ethical issues by discussing aspects of human existence and authenticity.
• Emmanuel Levinas: Levinas is renowned for his emphasis on ethics. He proposed that ethics is the first philosophy, where the relationship with the 'Other' (another person) is primary and fundamental to understanding human existence. This ethical priority distinguishes him from others on this list.
• Maurice Merleau-Ponty: Merleau-Ponty is also a phenomenologist but is better known for his contributions to the philosophy of perception and the embodiment of consciousness, without a primary focus on ethics.

From this analysis, the correct answer is Emmanuel Levinas, since he explicitly focused on the primacy of ethics in his philosophical work.

Conclusion: Emmanuel Levinas is the philosopher who stressed the importance of ethics, distinguishing it as the core of philosophical inquiry. His philosophy places ethics before ontology, making him unique among these philosophers in the emphasis of ethical considerations.