Deep narrow-band surveys have revealed a large population of faint Ly α emitters (LAEs) in the distant Universe, but relatively little is known about the most luminous sources ( erg s⁻¹; ). Here we present the spectroscopic follow-up of 21 luminous LAEs at z ∼ 2–3 found with panoramic narrow-band surveys over five independent extragalactic fields (≈4 × 10⁶ Mpc³ surveyed at z ∼ 2.2 and z ∼ 3.1). We use WHT/ISIS, Keck/DEIMOS, and VLT/X-SHOOTER to study these sources using high ionization UV lines. Luminous LAEs at z ∼ 2–3 have blue UV slopes () and high Ly α escape fractions ( per cent) and span five orders of magnitude in UV luminosity (M_UV ≈ −19 to −24). Many (70 per cent) show at least one high ionization rest-frame UV line such as C iv, N v, C iii], He ii or O iii], typically blue-shifted by ≈100–200 km s⁻¹ relative to Ly α. Their Ly α profiles reveal a wide variety of shapes, including significant blue-shifted components and widths from 200 to 4000 km s⁻¹. Overall, 60 ± 11  per cent appear to be active galactic nucleus (AGN) dominated, and at L_Lyα > 10^43.3 erg s⁻¹ and/or M_UV < −21.5 virtually all LAEs are AGNs with high ionization parameters (log U = 0.6 ± 0.5) and with metallicities of ≈0.5 − 1 Z_⊙. Those lacking signatures of AGNs (40 ± 11  per cent) have lower ionization parameters ( and log ξ_ion = 25.4 ± 0.2) and are apparently metal-poor sources likely powered by young, dust-poor ‘maximal’ starbursts. Our results show that luminous LAEs at z ∼ 2–3 are a diverse population and that and mark a sharp transition in the nature of LAEs, from star formation dominated to AGN dominated.