Iron-based superconductors have grown to be a new continent of high T c superconductors comparable to cuprates. The optimal critical temperature ( T c) of 56 K in electron-doped 1111-type iron oxypnictides attracts considerable attention of physicists and chemists. Carrier doping is not only essential to induce superconductivity but also is a critical parameter that governs the electronic, magnetic, and crystallographic properties of ground states in high- T c superconductors. Hydride ion (H−) which is an anionic state of hydrogen acts as an efficient electron donor in the 1111-type, leading to several important discoveries such as two-dome structure of superconducting phase and bipartite parent phase. This article summarizes the synthesis,... physical properties, and electronic structure of the H− bearing 1111-type iron-based superconductors along with the relevant phenomena of other superconductors. We show several common characteristics of iron-based superconductors with high- T c over 50 K and suggest a way to achieve higher T c.