Jupiter Optimus MaximusGods/Godesses Index
The temple for the aspect of Jupiter known as Jupiter Optimus Maximus (the best and greatest) was located on the Capitoline Hill in honor of a vow made by Tarquinius Priscus in his wars against the Sabines. Jupiter Optimus Maximus is abbreviated IOM. he was also known as Jupiter Highest and Most Supreme (Juppiter Summus Exsuperantissimus). The Ludi Romani, held in September were in honor of Jupiter Optimus Maximus. A festival for him was held on the Ides of September. Together with Juno Regina and Minerva, he was part of the Capitoline Triad. The three deities shared temples called Capitolia.
Source: Adkins and Adkins Dictionary of Roman Religion.