Ethical Altruism is notoriously self-disregarding; striving to fulfill others' (strangers') interests even if it's done at the expense of oneself. An act is morally admissible if its consequences carry more benefits (over harms) to everyone except the agent.
Ethical Egoism is notoriously self-obsessive; striving to fulfill one's own interests even when doing so comes at the expense of everyone else. An act is morally admissible if its consequences carry more benefits (over harms) only to the agent.
Utilitarianism is self-inclusive and other-regarding. Everyone's interests have equal weightiness in proportion to their respective situation. Agents impacting a certain state of affairs don't rule themselves out and freely accommodate their own interests into the final harms/benefits distribution.