AlphaLacertae, also named Stellio, is a single white-hued star in the constellation of Lacerta, located 103light-years from the Sun. It is the brightest star in Lacerta with an apparent visual magnitude of 3.76. The star is moving closer to the Earth with a heliocentric radial velocity of −4.5km/s.

This is an ordinary A-type main-sequence star with a stellar classification of A1V, which indicates it is generating energy through hydrogen fusion at its core. It is around 400million years old with a relatively high rate of spin, showing a projected rotational velocity of 128km/s. The star has 2.2 times the mass of the Sun and 2.1 times the Sun's radius. It is radiating 28 times the Sun's luminosity from its photosphere at an effective temperature of .

AlphaLacertae has a visual companion, CCDM J22313+5017B, of spectral type A and apparent visual magnitude 11.8, approximately 36 arcseconds away. The companion is optical, a chance line-of-sight coincidence.

Naming

AlphaLacertae, Latinised from αLacertae, is the Bayer designation for this star; it has the Flamsteed designation 7Lacertae.

In Chinese astronomy, (), meaning Flying Serpent, refers to an asterism consisting of α Lacertae, 4 Lacertae, π2 Cygni, π1 Cygni, HD 206267, ε Cephei, β Lacertae, σ Cassiopeiae, ρ Cassiopeiae, τ Cassiopeiae, AR Cassiopeiae, 9 Lacertae, 3 Andromedae, 7 Andromedae, 8 Andromedae, λ Andromedae, κ Andromedae, ι Andromedae, and ψ Andromedae. Consequently, the Chinese name for α Lacertae itself is (, ).

The IAU Working Group on Star Names approved the name Stellio for this star on 29 August 2024 and it is now so entered in the IAU Catalog of Star Names. Stellio is an obsolete historical name for the constellation Lacerta, named after the lizard Laudakia stellio, the starred agama or stellion.

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