Tyrosine-protein kinase that acts as cell-surface receptor for angiopoietins and regulates angiogenesis, endothelial cell survival, proliferation, migration, adhesion and cell spreading, reorganization of the actin cytoskeleton, but also maintenance of vascular quiescence. Can activate or inhibit angiogenesis, depending on the context. Angiopoietin signaling triggers receptor dimerization and autophosphorylation at specific tyrosine residues that then serve as binding sites for scaffold proteins and effectors (By similarity).