Zelenskyy is set to address the gathering by video link and Stoltenberg will have an early lunch at the spring summit for leaders. BRUSSELS - NATO chief Jens Stoltenberg and Ukraine President Volodymyr Zelenskyy will be key figures at Thursday’s European Union summit, underscoring the importance the 27 EU leaders attach to protecting their eastern flank from Russian aggression and beefing up Ukraine’s defense capabilities.